diff --git a/app/Access/ExternalBaseUserProvider.php b/app/Access/ExternalBaseUserProvider.php
index ef001289d..8d82d28c8 100644
--- a/app/Access/ExternalBaseUserProvider.php
+++ b/app/Access/ExternalBaseUserProvider.php
@@ -48,7 +48,7 @@ class ExternalBaseUserProvider implements UserProvider
     /**
      * Retrieve a user by the given credentials.
      */
-    public function retrieveByCredentials(array $credentials): ?Authenticatable
+    public function retrieveByCredentials(array $credentials): ?User
     {
         return $this->userRepo->getByExternalAuthId($credentials['external_auth_id']);
     }
diff --git a/app/Access/Guards/ExternalBaseSessionGuard.php b/app/Access/Guards/ExternalBaseSessionGuard.php
index b38903182..4d263e581 100644
--- a/app/Access/Guards/ExternalBaseSessionGuard.php
+++ b/app/Access/Guards/ExternalBaseSessionGuard.php
@@ -50,8 +50,12 @@ class ExternalBaseSessionGuard implements StatefulGuard
     /**
      * Create a new authentication guard.
      */
-    public function __construct(string $name, UserProvider $provider, Session $session, RegistrationService $registrationService)
-    {
+    public function __construct(
+        string $name,
+        UserProvider $provider,
+        Session $session,
+        RegistrationService $registrationService
+    ) {
         $this->name = $name;
         $this->session = $session;
         $this->provider = $provider;
diff --git a/app/Access/Guards/LdapSessionGuard.php b/app/Access/Guards/LdapSessionGuard.php
index 9455d530d..f3628c897 100644
--- a/app/Access/Guards/LdapSessionGuard.php
+++ b/app/Access/Guards/LdapSessionGuard.php
@@ -83,6 +83,10 @@ class LdapSessionGuard extends ExternalBaseSessionGuard
             }
         }
 
+        if (!($user instanceof User)) {
+            throw new LoginAttemptException('Could not find or create a user for LDAP login.');
+        }
+
         // Sync LDAP groups if required
         if ($this->ldapService->shouldSyncGroups()) {
             $this->ldapService->syncGroups($user, $username);
diff --git a/app/Access/Oidc/OidcJwtWithClaims.php b/app/Access/Oidc/OidcJwtWithClaims.php
index 9d7eeead1..9763ab158 100644
--- a/app/Access/Oidc/OidcJwtWithClaims.php
+++ b/app/Access/Oidc/OidcJwtWithClaims.php
@@ -131,8 +131,6 @@ class OidcJwtWithClaims implements ProvidesClaims
             }
         }, $this->keys);
 
-        $parsedKeys = array_filter($parsedKeys);
-
         $contentToSign = $this->tokenParts[0] . '.' . $this->tokenParts[1];
         /** @var OidcJwtSigningKey $parsedKey */
         foreach ($parsedKeys as $parsedKey) {
diff --git a/app/Access/Oidc/OidcService.php b/app/Access/Oidc/OidcService.php
index a84bd3205..19120e2d3 100644
--- a/app/Access/Oidc/OidcService.php
+++ b/app/Access/Oidc/OidcService.php
@@ -80,6 +80,7 @@ class OidcService
         $provider->setPkceCode($pkceCode);
 
         // Try to exchange authorization code for access token
+        /** @var OidcAccessToken $accessToken */
         $accessToken = $provider->getAccessToken('authorization_code', [
             'code' => $authorizationCode,
         ]);
diff --git a/app/Activity/ActivityQueries.php b/app/Activity/ActivityQueries.php
index d5b047937..a3383e809 100644
--- a/app/Activity/ActivityQueries.php
+++ b/app/Activity/ActivityQueries.php
@@ -11,6 +11,7 @@ use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
 use BookStack\Users\Models\User;
 use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Relations\MorphTo;
 use Illuminate\Database\Eloquent\Relations\Relation;
 
@@ -27,6 +28,7 @@ class ActivityQueries
      */
     public function latest(int $count = 20, int $page = 0): array
     {
+        /** @var Collection<int, Activity> $activityList */
         $activityList = $this->permissions
             ->restrictEntityRelationQuery(Activity::query(), 'activities', 'loggable_id', 'loggable_type')
             ->orderBy('created_at', 'desc')
@@ -83,6 +85,7 @@ class ActivityQueries
      */
     public function userActivity(User $user, int $count = 20, int $page = 0): array
     {
+        /** @var Collection<int, Activity> $activityList */
         $activityList = $this->permissions
             ->restrictEntityRelationQuery(Activity::query(), 'activities', 'loggable_id', 'loggable_type')
             ->orderBy('created_at', 'desc')
diff --git a/app/Activity/Models/Comment.php b/app/Activity/Models/Comment.php
index 3faa76657..b49eb4564 100644
--- a/app/Activity/Models/Comment.php
+++ b/app/Activity/Models/Comment.php
@@ -3,6 +3,7 @@
 namespace BookStack\Activity\Models;
 
 use BookStack\App\Model;
+use BookStack\Entities\Models\Page;
 use BookStack\Permissions\Models\JointPermission;
 use BookStack\Permissions\PermissionApplicator;
 use BookStack\Users\Models\HasCreatorAndUpdater;
@@ -40,6 +41,9 @@ class Comment extends Model implements Loggable, OwnableInterface
 
     /**
      * Get the entity that this comment belongs to.
+     * It's only pages right now hence the typing below.
+     * Would need a deeper audit if that changes as many areas assume this is always a page.
+     * @return MorphTo<Page, $this>
      */
     public function entity(): MorphTo
     {
@@ -55,7 +59,9 @@ class Comment extends Model implements Loggable, OwnableInterface
 
         // Ultimately, we could just align the method name to 'commentable' but that would be a potential
         // breaking change and not really worthwhile in a patch due to the risk of creating extra problems.
-        return $this->morphTo(null, 'commentable_type', 'commentable_id');
+        /** @var MorphTo<Page, $this> $relation */
+        $relation = $this->morphTo(null, 'commentable_type', 'commentable_id');
+        return $relation;
     }
 
     /**
diff --git a/app/Activity/Tools/WebhookFormatter.php b/app/Activity/Tools/WebhookFormatter.php
index cb4e9cb0a..111efd5d4 100644
--- a/app/Activity/Tools/WebhookFormatter.php
+++ b/app/Activity/Tools/WebhookFormatter.php
@@ -73,13 +73,17 @@ class WebhookFormatter
         // Load entity owner, creator, updater details
         $this->addModelFormatter(
             fn ($event, $model) => ($model instanceof Entity),
-            fn ($model) => $model->load(['ownedBy', 'createdBy', 'updatedBy'])
+            function ($model) {
+                $model->load(['ownedBy', 'createdBy', 'updatedBy']);
+            }
         );
 
         // Load revision detail for page update and create events
         $this->addModelFormatter(
             fn ($event, $model) => ($model instanceof Page && ($event === ActivityType::PAGE_CREATE || $event === ActivityType::PAGE_UPDATE)),
-            fn ($model) => $model->load('currentRevision')
+            function ($model) {
+                $model->load('currentRevision');
+            }
         );
     }
 
diff --git a/app/Api/ApiDocsGenerator.php b/app/Api/ApiDocsGenerator.php
index 53cb2890a..8d1be79c8 100644
--- a/app/Api/ApiDocsGenerator.php
+++ b/app/Api/ApiDocsGenerator.php
@@ -138,8 +138,8 @@ class ApiDocsGenerator
             return $validation;
         }
 
-        if (is_object($validation) && method_exists($validation, '__toString')) {
-            return strval($validation);
+        if (is_object($validation) && $validation instanceof \Stringable) {
+            return $validation->__toString();
         }
 
         if ($validation instanceof Password) {
diff --git a/app/App/Providers/ThemeServiceProvider.php b/app/App/Providers/ThemeServiceProvider.php
index 671e5e1df..9b0f7001e 100644
--- a/app/App/Providers/ThemeServiceProvider.php
+++ b/app/App/Providers/ThemeServiceProvider.php
@@ -7,6 +7,7 @@ use BookStack\Theming\ThemeService;
 use BookStack\Theming\ThemeViews;
 use Illuminate\Support\Facades\Blade;
 use Illuminate\Support\ServiceProvider;
+use Illuminate\View\FileViewFinder;
 
 class ThemeServiceProvider extends ServiceProvider
 {
@@ -27,7 +28,11 @@ class ThemeServiceProvider extends ServiceProvider
         // Boot up the theme system
         $themeService = $this->app->make(ThemeService::class);
         $viewFactory = $this->app->make('view');
-        $themeViews = new ThemeViews($viewFactory->getFinder());
+        $viewFinder = $viewFactory->getFinder();
+        if (!($viewFinder instanceof FileViewFinder)) {
+            throw new \Exception('Only the file view finder is supported for the theme system');
+        }
+        $themeViews = new ThemeViews($viewFinder);
 
         // Use a custom include so that we can insert theme views before/after includes.
         // This is done, even if no theme is active, so that view caching does not create problems
diff --git a/app/App/helpers.php b/app/App/helpers.php
index 8f210ecaf..45a84da8d 100644
--- a/app/App/helpers.php
+++ b/app/App/helpers.php
@@ -6,6 +6,7 @@ use BookStack\Facades\Theme;
 use BookStack\Permissions\Permission;
 use BookStack\Permissions\PermissionApplicator;
 use BookStack\Settings\SettingService;
+use BookStack\Users\Models\OwnableInterface;
 use BookStack\Users\Models\User;
 
 /**
@@ -40,7 +41,7 @@ function user(): User
  * Check if the current user has a permission. If an ownable element
  * is passed in the jointPermissions are checked against that particular item.
  */
-function userCan(string|Permission $permission, ?Model $ownable = null): bool
+function userCan(string|Permission $permission, (Model&OwnableInterface)|null $ownable = null): bool
 {
     if (is_null($ownable)) {
         return user()->can($permission);
diff --git a/app/Entities/Controllers/PageApiController.php b/app/Entities/Controllers/PageApiController.php
index 38042e670..ca8989f07 100644
--- a/app/Entities/Controllers/PageApiController.php
+++ b/app/Entities/Controllers/PageApiController.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace BookStack\Entities\Controllers;
 
 use BookStack\Activity\Tools\CommentTree;
@@ -10,7 +12,9 @@ use BookStack\Exceptions\PermissionsException;
 use BookStack\Http\ApiController;
 use BookStack\Permissions\Permission;
 use Exception;
+use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
+use Illuminate\Http\Response;
 
 class PageApiController extends ApiController
 {
@@ -45,7 +49,7 @@ class PageApiController extends ApiController
     /**
      * Get a listing of pages visible to the user.
      */
-    public function list()
+    public function list(): JsonResponse
     {
         $pages = $this->queries->visibleForList()
             ->addSelect(['created_by', 'updated_by', 'revision_count', 'editor']);
@@ -69,7 +73,7 @@ class PageApiController extends ApiController
      * Any images included via base64 data URIs will be extracted and saved as gallery
      * images against the page during upload.
      */
-    public function create(Request $request)
+    public function create(Request $request): JsonResponse
     {
         $this->validate($request, $this->rules['create']);
 
@@ -102,9 +106,9 @@ class PageApiController extends ApiController
      * Comments for the page are provided in a tree-structure representing the hierarchy of top-level
      * comments and replies, for both archived and active comments.
      */
-    public function read(string $id)
+    public function read(string $id): JsonResponse
     {
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
 
         $page = $page->forJsonDisplay();
         $commentTree = (new CommentTree($page));
@@ -124,11 +128,11 @@ class PageApiController extends ApiController
      * Providing a 'book_id' or 'chapter_id' property will essentially move
      * the page into that parent element if you have permissions to do so.
      */
-    public function update(Request $request, string $id)
+    public function update(Request $request, string $id): JsonResponse
     {
         $requestData = $this->validate($request, $this->rules['update']);
 
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
         $this->checkOwnablePermission(Permission::PageUpdate, $page);
 
         $parent = null;
@@ -161,9 +165,9 @@ class PageApiController extends ApiController
      * Delete a page.
      * This will typically send the page to the recycle bin.
      */
-    public function delete(string $id)
+    public function delete(string $id): Response
     {
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
         $this->checkOwnablePermission(Permission::PageDelete, $page);
 
         $this->pageRepo->destroy($page);
diff --git a/app/Entities/Controllers/PageController.php b/app/Entities/Controllers/PageController.php
index 2cd9b0b16..10a46d58b 100644
--- a/app/Entities/Controllers/PageController.php
+++ b/app/Entities/Controllers/PageController.php
@@ -24,6 +24,7 @@ use BookStack\Util\HtmlContentFilter;
 use BookStack\Util\HtmlContentFilterConfig;
 use Exception;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\Relation;
 use Illuminate\Http\Request;
 use Illuminate\Validation\ValidationException;
 use Throwable;
@@ -364,8 +365,8 @@ class PageController extends Controller
      */
     public function showRecentlyUpdated()
     {
-        $visibleBelongsScope = function (BelongsTo $query) {
-            $query->scopes('visible');
+        $visibleBelongsScope = function (Relation $relation): void {
+            $relation->scopes('visible');
         };
 
         $pages = $this->queries->visibleForList()
diff --git a/app/Entities/Controllers/PageRevisionController.php b/app/Entities/Controllers/PageRevisionController.php
index cc6b79bfe..801aeed3e 100644
--- a/app/Entities/Controllers/PageRevisionController.php
+++ b/app/Entities/Controllers/PageRevisionController.php
@@ -177,7 +177,7 @@ class PageRevisionController extends Controller
      */
     public function destroyUserDraft(string $pageId)
     {
-        $page = $this->pageQueries->findVisibleByIdOrFail($pageId);
+        $page = $this->pageQueries->findVisibleByIdOrFail(intval($pageId));
         $this->revisionRepo->deleteDraftsForCurrentUser($page);
 
         return response('', 200);
diff --git a/app/Entities/Models/Book.php b/app/Entities/Models/Book.php
index 10f04695a..abb081d71 100644
--- a/app/Entities/Models/Book.php
+++ b/app/Entities/Models/Book.php
@@ -20,10 +20,10 @@ use Illuminate\Support\Collection;
  * @property ?int                                     $image_id
  * @property ?int                                     $default_template_id
  * @property ?int                                     $sort_rule_id
- * @property \Illuminate\Database\Eloquent\Collection $chapters
- * @property \Illuminate\Database\Eloquent\Collection $pages
- * @property \Illuminate\Database\Eloquent\Collection $directPages
- * @property \Illuminate\Database\Eloquent\Collection $shelves
+ * @property \Illuminate\Database\Eloquent\Collection<int, Chapter> $chapters
+ * @property \Illuminate\Database\Eloquent\Collection<int, Page> $pages
+ * @property \Illuminate\Database\Eloquent\Collection<int, Page> $directPages
+ * @property \Illuminate\Database\Eloquent\Collection<int, Bookshelf> $shelves
  * @property ?SortRule                                $sortRule
  */
 class Book extends Entity implements HasDescriptionInterface, HasCoverInterface, HasDefaultTemplateInterface
diff --git a/app/Entities/Models/Entity.php b/app/Entities/Models/Entity.php
index 27cfccaa8..296bd3a66 100644
--- a/app/Entities/Models/Entity.php
+++ b/app/Entities/Models/Entity.php
@@ -46,7 +46,7 @@ use Illuminate\Database\Eloquent\SoftDeletes;
  * @property int|null   $created_by
  * @property int|null   $updated_by
  * @property int|null   $owned_by
- * @property Collection $tags
+ * @property Collection<int, Tag> $tags
  *
  * @method static Entity|Builder visible()
  * @method static Builder withLastView()
diff --git a/app/Entities/Models/Page.php b/app/Entities/Models/Page.php
index d3a392da6..c38f33af3 100644
--- a/app/Entities/Models/Page.php
+++ b/app/Entities/Models/Page.php
@@ -24,8 +24,8 @@ use Illuminate\Database\Eloquent\Relations\HasOne;
  * @property int          $revision_count
  * @property string       $editor
  * @property Chapter|null $chapter
- * @property Collection   $attachments
- * @property Collection   $revisions
+ * @property Collection<int, Attachment>   $attachments
+ * @property Collection<int, PageRevision>   $revisions
  * @property PageRevision $currentRevision
  */
 class Page extends BookChild
diff --git a/app/Entities/Queries/QueryPopular.php b/app/Entities/Queries/QueryPopular.php
index 065ae82ef..1782070de 100644
--- a/app/Entities/Queries/QueryPopular.php
+++ b/app/Entities/Queries/QueryPopular.php
@@ -6,6 +6,7 @@ use BookStack\Activity\Models\View;
 use BookStack\Entities\EntityProvider;
 use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Facades\DB;
 
@@ -20,6 +21,7 @@ class QueryPopular
 
     public function run(int $count, int $page, array $filterModels): Collection
     {
+        /** @var Builder<View> $query */
         $query = $this->permissions
             ->restrictEntityRelationQuery(View::query(), 'views', 'viewable_id', 'viewable_type')
             ->select('*', 'viewable_id', 'viewable_type', DB::raw('SUM(views) as view_count'))
diff --git a/app/Entities/Queries/QueryRecentlyViewed.php b/app/Entities/Queries/QueryRecentlyViewed.php
index f28b8f865..8ba1a57ba 100644
--- a/app/Entities/Queries/QueryRecentlyViewed.php
+++ b/app/Entities/Queries/QueryRecentlyViewed.php
@@ -5,6 +5,7 @@ namespace BookStack\Entities\Queries;
 use BookStack\Activity\Models\View;
 use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Support\Collection;
 
 class QueryRecentlyViewed
@@ -22,6 +23,7 @@ class QueryRecentlyViewed
             return collect();
         }
 
+        /** @var Builder<View> $query */
         $query = $this->permissions->restrictEntityRelationQuery(
             View::query(),
             'views',
diff --git a/app/Entities/Queries/QueryTopFavourites.php b/app/Entities/Queries/QueryTopFavourites.php
index 6340e35ef..2719e94bc 100644
--- a/app/Entities/Queries/QueryTopFavourites.php
+++ b/app/Entities/Queries/QueryTopFavourites.php
@@ -5,6 +5,7 @@ namespace BookStack\Entities\Queries;
 use BookStack\Activity\Models\Favourite;
 use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Query\JoinClause;
 
 class QueryTopFavourites
@@ -22,6 +23,7 @@ class QueryTopFavourites
             return collect();
         }
 
+        /** @var Builder<Favourite> $query */
         $query = $this->permissions
             ->restrictEntityRelationQuery(Favourite::query(), 'favourites', 'favouritable_id', 'favouritable_type')
             ->select('favourites.*')
diff --git a/app/Entities/Tools/Markdown/CustomListItemRenderer.php b/app/Entities/Tools/Markdown/CustomListItemRenderer.php
index 0c506d7f9..14cdaa2ea 100644
--- a/app/Entities/Tools/Markdown/CustomListItemRenderer.php
+++ b/app/Entities/Tools/Markdown/CustomListItemRenderer.php
@@ -25,9 +25,13 @@ class CustomListItemRenderer implements NodeRendererInterface
      */
     public function render(Node $node, ChildNodeRendererInterface $childRenderer)
     {
+        if (!($node instanceof ListItem)) {
+            return null;
+        }
+
         $listItem = $this->baseRenderer->render($node, $childRenderer);
 
-        if ($node instanceof ListItem && $this->startsTaskListItem($node) && $listItem instanceof HtmlElement) {
+        if ($this->startsTaskListItem($node) && $listItem instanceof HtmlElement) {
             $listItem->setAttribute('class', 'task-list-item');
         }
 
diff --git a/app/Entities/Tools/PageContent.php b/app/Entities/Tools/PageContent.php
index 9fb4596f5..c66dcbe41 100644
--- a/app/Entities/Tools/PageContent.php
+++ b/app/Entities/Tools/PageContent.php
@@ -421,28 +421,41 @@ class PageContent
      */
     protected function headerNodesToLevelList(DOMNodeList $nodeList): array
     {
-        $tree = collect($nodeList)->map(function (DOMElement $header) {
+        $minLevel = 6;
+
+        $headerDetails = array_map(function (DOMNode $header) use (&$minLevel) {
+            if (!$header instanceof DOMElement) {
+                return null;
+            }
+
             $text = trim(str_replace("\xc2\xa0", ' ', $header->nodeValue));
             $text = mb_substr($text, 0, 100);
 
+            if (empty($text)) {
+                return null;
+            }
+
+            $level = intval(str_replace('h', '', $header->nodeName));
+            if ($level < $minLevel) {
+                $minLevel = $level;
+            }
+
             return [
                 'nodeName' => strtolower($header->nodeName),
-                'level'    => intval(str_replace('h', '', $header->nodeName)),
+                'level'    => $level,
                 'link'     => '#' . $header->getAttribute('id'),
                 'text'     => $text,
             ];
-        })->filter(function ($header) {
-            return mb_strlen($header['text']) > 0;
-        });
+        }, [...$nodeList]);
+
+        $filtered = array_values(array_filter($headerDetails));
 
         // Shift headers if only smaller headers have been used
-        $levelChange = ($tree->pluck('level')->min() - 1);
-        $tree = $tree->map(function ($header) use ($levelChange) {
-            $header['level'] -= ($levelChange);
+        $levelChange = ($minLevel - 1);
+        foreach ($filtered as $index => $header) {
+            $filtered[$index]['level'] -= $levelChange;
+        }
 
-            return $header;
-        });
-
-        return $tree->toArray();
+        return $filtered;
     }
 }
diff --git a/app/Entities/Tools/PageIncludeParser.php b/app/Entities/Tools/PageIncludeParser.php
index af7ed4fc6..16917f41c 100644
--- a/app/Entities/Tools/PageIncludeParser.php
+++ b/app/Entities/Tools/PageIncludeParser.php
@@ -192,10 +192,10 @@ class PageIncludeParser
     /**
      * Get the parent paragraph of the given node, if existing.
      */
-    protected function getParentParagraph(DOMNode $parent): ?DOMNode
+    protected function getParentParagraph(DOMNode $parent): ?DOMElement
     {
         do {
-            if (strtolower($parent->nodeName) === 'p') {
+            if (strtolower($parent->nodeName) === 'p' && $parent instanceof DOMElement) {
                 return $parent;
             }
 
diff --git a/app/Entities/Tools/SlugGenerator.php b/app/Entities/Tools/SlugGenerator.php
index 6eec84a91..ac003b97a 100644
--- a/app/Entities/Tools/SlugGenerator.php
+++ b/app/Entities/Tools/SlugGenerator.php
@@ -52,7 +52,7 @@ class SlugGenerator
     {
         $slug = Str::slug($name);
         if ($slug === '') {
-            $slug = substr(md5(rand(1, 500)), 0, 5);
+            $slug = substr(md5(strval(rand(1, 500))), 0, 5);
         }
 
         return $slug;
diff --git a/app/Exports/ImportRepo.php b/app/Exports/ImportRepo.php
index 79db69fca..ed631409b 100644
--- a/app/Exports/ImportRepo.php
+++ b/app/Exports/ImportRepo.php
@@ -3,6 +3,8 @@
 namespace BookStack\Exports;
 
 use BookStack\Activity\ActivityType;
+use BookStack\Entities\Models\Book;
+use BookStack\Entities\Models\Chapter;
 use BookStack\Entities\Models\Entity;
 use BookStack\Entities\Queries\EntityQueries;
 use BookStack\Exceptions\FileUploadException;
@@ -119,6 +121,9 @@ class ImportRepo
         $parentModel = null;
         if ($import->type === 'page' || $import->type === 'chapter') {
             $parentModel = $parent ? $this->entityQueries->findVisibleByStringIdentifier($parent) : null;
+            if ($parentModel && !($parentModel instanceof Book || $parentModel instanceof Chapter)) {
+                throw new ZipImportException(['Selected parent is not a book or chapter']);
+            }
         }
 
         DB::beginTransaction();
diff --git a/app/Exports/ZipExports/ZipImportRunner.php b/app/Exports/ZipExports/ZipImportRunner.php
index 7a53e01f4..41e9038ad 100644
--- a/app/Exports/ZipExports/ZipImportRunner.php
+++ b/app/Exports/ZipExports/ZipImportRunner.php
@@ -48,7 +48,7 @@ class ZipImportRunner
      * Returns the top-level entity item which was imported.
      * @throws ZipImportException
      */
-    public function run(Import $import, ?Entity $parent = null): Entity
+    public function run(Import $import, Book|Chapter|null $parent = null): Entity
     {
         $zipPath = $this->getZipPath($import);
         $reader = new ZipExportReader($zipPath);
diff --git a/app/Http/Controller.php b/app/Http/Controller.php
index 796505795..09c38ee61 100644
--- a/app/Http/Controller.php
+++ b/app/Http/Controller.php
@@ -7,6 +7,7 @@ use BookStack\App\Model;
 use BookStack\Exceptions\NotifyException;
 use BookStack\Facades\Activity;
 use BookStack\Permissions\Permission;
+use BookStack\Users\Models\OwnableInterface;
 use Illuminate\Foundation\Bus\DispatchesJobs;
 use Illuminate\Foundation\Validation\ValidatesRequests;
 use Illuminate\Http\JsonResponse;
@@ -80,7 +81,7 @@ abstract class Controller extends BaseController
     /**
      * Check the current user's permissions against an ownable item otherwise throw an exception.
      */
-    protected function checkOwnablePermission(string|Permission $permission, Model $ownable, string $redirectLocation = '/'): void
+    protected function checkOwnablePermission(string|Permission $permission, Model&OwnableInterface $ownable, string $redirectLocation = '/'): void
     {
         if (!userCan($permission, $ownable)) {
             $this->showPermissionError($redirectLocation);
diff --git a/app/Permissions/JointPermissionBuilder.php b/app/Permissions/JointPermissionBuilder.php
index 1788124cd..101e3a00f 100644
--- a/app/Permissions/JointPermissionBuilder.php
+++ b/app/Permissions/JointPermissionBuilder.php
@@ -105,6 +105,7 @@ class JointPermissionBuilder
 
     /**
      * Get a query for fetching a book with its children.
+     * @return Builder<Book>
      */
     protected function bookFetchQuery(): Builder
     {
@@ -121,9 +122,11 @@ class JointPermissionBuilder
 
     /**
      * Build joint permissions for the given book and role combinations.
+     * @param EloquentCollection<int, Book> $books
      */
     protected function buildJointPermissionsForBooks(EloquentCollection $books, array $roles, bool $deleteOld = false): void
     {
+        /** @var EloquentCollection<int, Entity> $entities */
         $entities = clone $books;
 
         /** @var Book $book */
diff --git a/app/References/Reference.php b/app/References/Reference.php
index df8a3a789..602e19eab 100644
--- a/app/References/Reference.php
+++ b/app/References/Reference.php
@@ -2,8 +2,8 @@
 
 namespace BookStack\References;
 
+use BookStack\App\Model;
 use BookStack\Permissions\Models\JointPermission;
-use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\Relations\MorphTo;
 
diff --git a/app/References/ReferenceFetcher.php b/app/References/ReferenceFetcher.php
index 8588c6e2c..0c76b4698 100644
--- a/app/References/ReferenceFetcher.php
+++ b/app/References/ReferenceFetcher.php
@@ -22,6 +22,7 @@ class ReferenceFetcher
      */
     public function getReferencesToEntity(Entity $entity, bool $withContents = false): Collection
     {
+        /** @var Collection<int, Reference> $references */
         $references = $this->queryReferencesToEntity($entity)->get();
         $this->mixedEntityListLoader->loadIntoRelations($references->all(), 'from', false, $withContents);
 
@@ -37,6 +38,9 @@ class ReferenceFetcher
         return $this->queryReferencesToEntity($entity)->count();
     }
 
+    /**
+     * @return Builder<Reference>
+     */
     protected function queryReferencesToEntity(Entity $entity): Builder
     {
         $baseQuery = Reference::query()
diff --git a/app/Search/SearchRunner.php b/app/Search/SearchRunner.php
index d49cb439a..60d111d08 100644
--- a/app/Search/SearchRunner.php
+++ b/app/Search/SearchRunner.php
@@ -4,6 +4,7 @@ namespace BookStack\Search;
 
 use BookStack\Entities\EntityProvider;
 use BookStack\Entities\Models\Entity;
+use BookStack\Entities\Models\EntityTable;
 use BookStack\Entities\Queries\EntityQueries;
 use BookStack\Entities\Tools\EntityHydrator;
 use BookStack\Permissions\PermissionApplicator;
@@ -90,6 +91,8 @@ class SearchRunner
 
     /**
      * Get a page of result data from the given query based on the provided page parameters.
+     * @param EloquentBuilder<EntityTable> $query
+     * @return Collection<Entity>
      */
     protected function getPageOfDataFromQuery(EloquentBuilder $query, int $page, int $count): Collection
     {
@@ -106,6 +109,7 @@ class SearchRunner
     /**
      * Create a search query for an entity.
      * @param string[] $entityTypes
+     * @return EloquentBuilder<EntityTable>
      */
     protected function buildQuery(SearchOptions $searchOpts, array $entityTypes): EloquentBuilder
     {
diff --git a/app/Settings/SettingService.php b/app/Settings/SettingService.php
index a86730c1b..e3112e9c7 100644
--- a/app/Settings/SettingService.php
+++ b/app/Settings/SettingService.php
@@ -243,9 +243,9 @@ class SettingService
     /**
      * Convert a setting key into a user-specific key.
      */
-    protected function userKey(string $userId, string $key = ''): string
+    protected function userKey(int $userId, string $key = ''): string
     {
-        return 'user:' . $userId . ':' . $key;
+        return 'user:' . strval($userId) . ':' . $key;
     }
 
     /**
@@ -275,7 +275,7 @@ class SettingService
     /**
      * Delete settings for a given user id.
      */
-    public function deleteUserSettings(string $userId): void
+    public function deleteUserSettings(int $userId): void
     {
         Setting::query()
             ->where('setting_key', 'like', $this->userKey($userId) . '%')
diff --git a/app/Sorting/SortRule.php b/app/Sorting/SortRule.php
index bf53365a2..ffe2d4115 100644
--- a/app/Sorting/SortRule.php
+++ b/app/Sorting/SortRule.php
@@ -38,21 +38,35 @@ class SortRule extends Model implements Loggable
         $this->sequence = implode(',', $values);
     }
 
+    /**
+     * @inheritDoc
+     */
     public function logDescriptor(): string
     {
         return "({$this->id}) {$this->name}";
     }
 
+    /**
+     * Get the URL to where this rule can be managed.
+     */
     public function getUrl(): string
     {
         return url("/settings/sorting/rules/{$this->id}");
     }
 
+    /**
+     * Get the books which are specifically set to use this sort rule.
+     * @return HasMany<Book, $this>
+     */
     public function books(): HasMany
     {
         return $this->hasMany(Book::class, 'entity_container_data.sort_rule_id', 'id');
     }
 
+    /**
+     * Get all the available sort rules, ordered by name, with the number of books using each.
+     * @return Collection<SortRule>
+     */
     public static function allByName(): Collection
     {
         return static::query()
diff --git a/app/Uploads/AttachmentService.php b/app/Uploads/AttachmentService.php
index dabd53729..3de84bdd0 100644
--- a/app/Uploads/AttachmentService.php
+++ b/app/Uploads/AttachmentService.php
@@ -102,7 +102,7 @@ class AttachmentService
     /**
      * Updates the ordering for a listing of attached files.
      */
-    public function updateFileOrderWithinPage(array $attachmentOrder, string $pageId)
+    public function updateFileOrderWithinPage(array $attachmentOrder, int $pageId)
     {
         foreach ($attachmentOrder as $index => $attachmentId) {
             Attachment::query()->where('uploaded_to', '=', $pageId)
diff --git a/app/Users/Controllers/RoleApiController.php b/app/Users/Controllers/RoleApiController.php
index 93ecc549b..6f0c59651 100644
--- a/app/Users/Controllers/RoleApiController.php
+++ b/app/Users/Controllers/RoleApiController.php
@@ -87,7 +87,7 @@ class RoleApiController extends ApiController
      */
     public function read(string $id)
     {
-        $role = $this->permissionsRepo->getRoleById($id);
+        $role = $this->permissionsRepo->getRoleById(intval($id));
         $this->singleFormatter($role);
 
         return response()->json($role);
diff --git a/app/Users/Controllers/RoleController.php b/app/Users/Controllers/RoleController.php
index b9f06dace..56a6c7416 100644
--- a/app/Users/Controllers/RoleController.php
+++ b/app/Users/Controllers/RoleController.php
@@ -94,7 +94,7 @@ class RoleController extends Controller
     public function edit(string $id)
     {
         $this->checkPermission(Permission::UserRolesManage);
-        $role = $this->permissionsRepo->getRoleById($id);
+        $role = $this->permissionsRepo->getRoleById(intval($id));
 
         $this->setPageTitle(trans('settings.role_edit'));
 
@@ -129,7 +129,7 @@ class RoleController extends Controller
     public function showDelete(string $id)
     {
         $this->checkPermission(Permission::UserRolesManage);
-        $role = $this->permissionsRepo->getRoleById($id);
+        $role = $this->permissionsRepo->getRoleById(intval($id));
         $roles = $this->permissionsRepo->getAllRolesExcept($role);
         $blankRole = $role->newInstance(['display_name' => trans('settings.role_delete_no_migration')]);
         $roles->prepend($blankRole);
@@ -151,7 +151,7 @@ class RoleController extends Controller
 
         try {
             $migrateRoleId = intval($request->input('migrate_role_id') ?: "0");
-            $this->permissionsRepo->deleteRole($id, $migrateRoleId);
+            $this->permissionsRepo->deleteRole(intval($id), $migrateRoleId);
         } catch (PermissionsException $e) {
             $this->showErrorNotification($e->getMessage());
 
diff --git a/app/Users/Controllers/UserApiController.php b/app/Users/Controllers/UserApiController.php
index ebc17e262..07eefadc7 100644
--- a/app/Users/Controllers/UserApiController.php
+++ b/app/Users/Controllers/UserApiController.php
@@ -110,7 +110,7 @@ class UserApiController extends ApiController
      */
     public function read(string $id)
     {
-        $user = $this->userRepo->getById($id);
+        $user = $this->userRepo->getById(intval($id));
         $this->singleFormatter($user);
 
         return response()->json($user);
@@ -124,8 +124,8 @@ class UserApiController extends ApiController
      */
     public function update(Request $request, string $id)
     {
-        $data = $this->validate($request, $this->rules($id)['update']);
-        $user = $this->userRepo->getById($id);
+        $data = $this->validate($request, $this->rules(intval($id))['update']);
+        $user = $this->userRepo->getById(intval($id));
         $this->userRepo->update($user, $data, userCan(Permission::UsersManage));
         $this->singleFormatter($user);
 
@@ -140,7 +140,7 @@ class UserApiController extends ApiController
      */
     public function delete(Request $request, string $id)
     {
-        $user = $this->userRepo->getById($id);
+        $user = $this->userRepo->getById(intval($id));
         $newOwnerId = $request->input('migrate_ownership_id', null);
 
         $this->userRepo->destroy($user, $newOwnerId);
diff --git a/app/Util/DatabaseTransaction.php b/app/Util/DatabaseTransaction.php
index e36bd2ef3..2e57b6479 100644
--- a/app/Util/DatabaseTransaction.php
+++ b/app/Util/DatabaseTransaction.php
@@ -3,6 +3,7 @@
 namespace BookStack\Util;
 
 use Closure;
+use Illuminate\Database\Connection;
 use Illuminate\Support\Facades\DB;
 use Throwable;
 
@@ -24,7 +25,7 @@ use Throwable;
 class DatabaseTransaction
 {
     /**
-     * @param  (Closure(static): TReturn)  $callback
+     * @param  (Closure(Connection): TReturn)  $callback
      */
     public function __construct(
         protected Closure $callback
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index bab28ea0e..54403adfe 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -7,7 +7,7 @@ parameters:
         - app
 
     # The level 8 is the highest level
-    level: 4
+    level: 5
 
     phpVersion:
         min: 80200