diff --git a/typo3/sysext/core/Classes/Resource/Driver/DriverInterface.php b/typo3/sysext/core/Classes/Resource/Driver/DriverInterface.php
index c522cb758b390e4a44fedf1e8d025e3d37a8cbd9..78d04e5ebf21a45a49d45b7503a11aa003942921 100644
--- a/typo3/sysext/core/Classes/Resource/Driver/DriverInterface.php
+++ b/typo3/sysext/core/Classes/Resource/Driver/DriverInterface.php
@@ -437,7 +437,8 @@ interface DriverInterface
      *                     If a driver does not support the given property, it
      *                     should fall back to "name".
      * @param bool $sortRev TRUE to indicate reverse sorting (last to first)
-     * @return array of Folder Identifier
+     * @return array<string|int, string> folder identifiers (where key and value are identical, but int-like identifiers
+     *         will get converted to int array keys)
      */
     public function getFoldersInFolder($folderIdentifier, $start = 0, $numberOfItems = 0, $recursive = false, array $folderNameFilterCallbacks = [], $sort = '', $sortRev = false);
 
diff --git a/typo3/sysext/core/Classes/Resource/Driver/LocalDriver.php b/typo3/sysext/core/Classes/Resource/Driver/LocalDriver.php
index cc934127817a6198582f0f09b2e81145bfe88bab..b2d85a9d15931536d2582c9642c426f8e0d139a8 100644
--- a/typo3/sysext/core/Classes/Resource/Driver/LocalDriver.php
+++ b/typo3/sysext/core/Classes/Resource/Driver/LocalDriver.php
@@ -356,7 +356,8 @@ class LocalDriver extends AbstractHierarchicalFilesystemDriver implements Stream
      *                     If a driver does not support the given property, it
      *                     should fall back to "name".
      * @param bool $sortRev TRUE to indicate reverse sorting (last to first)
-     * @return array
+     * @return array<string|int, string> folder identifiers (where key and value are identical, but int-like identifiers
+     *         will get converted to int array keys)
      * @throws \InvalidArgumentException
      */
     protected function getDirectoryItemList($folderIdentifier, $start, $numberOfItems, array $filterMethods, $includeFiles = true, $includeDirs = true, $recursive = false, $sort = '', $sortRev = false)
@@ -399,6 +400,7 @@ class LocalDriver extends AbstractHierarchicalFilesystemDriver implements Stream
                 if ($start > 0) {
                     $start--;
                 } else {
+                    // The identifier can also be an int-like string, resulting in int array keys.
                     $items[$iteratorItem['identifier']] = $iteratorItem['identifier'];
                     // Decrement item counter to make sure we only return $numberOfItems
                     // we cannot do this earlier in the method (unlike moving the iterator forward) because we only add the
@@ -503,7 +505,8 @@ class LocalDriver extends AbstractHierarchicalFilesystemDriver implements Stream
      *                     If a driver does not support the given property, it
      *                     should fall back to "name".
      * @param bool $sortRev TRUE to indicate reverse sorting (last to first)
-     * @return array of Folder Identifier
+     * @return array<string|int, string> folder identifiers (where key and value are identical, but int-like identifiers
+     *         will get converted to int array keys)
      */
     public function getFoldersInFolder($folderIdentifier, $start = 0, $numberOfItems = 0, $recursive = false, array $folderNameFilterCallbacks = [], $sort = '', $sortRev = false)
     {
diff --git a/typo3/sysext/core/Classes/Resource/Folder.php b/typo3/sysext/core/Classes/Resource/Folder.php
index a547cc694dc073112668875a42aa83899d8d65c4..20d37cb6f94c21df57198044e5e60c12a272b66f 100644
--- a/typo3/sysext/core/Classes/Resource/Folder.php
+++ b/typo3/sysext/core/Classes/Resource/Folder.php
@@ -282,13 +282,11 @@ class Folder implements FolderInterface
     }
 
     /**
-     * Returns a list of subfolders
-     *
      * @param int $start The item to start at
      * @param int $numberOfItems The number of items to return
      * @param int $filterMode The filter mode to use for the filelist.
      * @param bool $recursive
-     * @return Folder[]
+     * @return array<string|int, Folder>
      */
     public function getSubfolders($start = 0, $numberOfItems = 0, $filterMode = self::FILTER_MODE_USE_OWN_AND_STORAGE_FILTERS, $recursive = false)
     {
diff --git a/typo3/sysext/core/Classes/Resource/FolderInterface.php b/typo3/sysext/core/Classes/Resource/FolderInterface.php
index 59ca1d43d15730f938daf4bbf2702e14787eb785..aaed937479d1aac366686d06a6512b245b8797c6 100644
--- a/typo3/sysext/core/Classes/Resource/FolderInterface.php
+++ b/typo3/sysext/core/Classes/Resource/FolderInterface.php
@@ -33,9 +33,7 @@ interface FolderInterface extends ResourceInterface
     const ROLE_USER_MOUNT = 'user-mount';
 
     /**
-     * Returns a list of all subfolders
-     *
-     * @return Folder[]
+     * @return array<string|int, Folder>
      */
     public function getSubfolders();
 
diff --git a/typo3/sysext/core/Classes/Resource/ResourceStorage.php b/typo3/sysext/core/Classes/Resource/ResourceStorage.php
index 246b2f08a8f5d18ff35c64d090de4b46dc1eeb5c..0de4937d9c773c1edabc78f45957217a342678bc 100644
--- a/typo3/sysext/core/Classes/Resource/ResourceStorage.php
+++ b/typo3/sysext/core/Classes/Resource/ResourceStorage.php
@@ -2427,7 +2427,7 @@ class ResourceStorage implements ResourceStorageInterface
      *                     If a driver does not support the given property, it
      *                     should fall back to "name".
      * @param bool $sortRev TRUE to indicate reverse sorting (last to first)
-     * @return Folder[]
+     * @return array<string|int, Folder>
      */
     public function getFoldersInFolder(Folder $folder, $start = 0, $maxNumberOfItems = 0, $useFilters = true, $recursive = false, $sort = '', $sortRev = false)
     {
@@ -2445,6 +2445,7 @@ class ResourceStorage implements ResourceStorageInterface
 
         $folders = [];
         foreach ($folderIdentifiers as $folderIdentifier) {
+            // The folder identifier can also be an int-like string, resulting in int array keys.
             $folders[$folderIdentifier] = $this->getFolder($folderIdentifier, true);
         }
         return $folders;
diff --git a/typo3/sysext/core/Classes/Resource/Utility/ListUtility.php b/typo3/sysext/core/Classes/Resource/Utility/ListUtility.php
index b5a6530c6e4051f593e2c172fa7c704de2bb93e7..4809e973ec98192924272d322ee57a5e954b60cc 100644
--- a/typo3/sysext/core/Classes/Resource/Utility/ListUtility.php
+++ b/typo3/sysext/core/Classes/Resource/Utility/ListUtility.php
@@ -28,7 +28,7 @@ class ListUtility
      * Resolve special folders (by their role) into localised string
      *
      * @param Folder[] $folders
-     * @return array<string, Folder> array with Folders using the Folder name (with our without role) as key
+     * @return array<string|int, Folder> Folders using the Folder name (with or without role) as key
      */
     public static function resolveSpecialFolderNames(array $folders)
     {