diff -u b/core/modules/media/src/Entity/Media.php b/core/modules/media/src/Entity/Media.php
--- b/core/modules/media/src/Entity/Media.php
+++ b/core/modules/media/src/Entity/Media.php
@@ -211,17 +211,17 @@
   }
 
   /**
-   * Gets a file URI for the thumbnail of a media item.
+   * Gets the URI for the thumbnail of a media item.
    *
-   * If thumbnail fetching should be queued then temporary use default
-   * thumbnail for new files or temporary keep existing thumbnail for
-   * updates.
-   * Immediately fetch a new thumbnail from the media source otherwise.
+   * If thumbnail fetching is queued, new media items will use the default
+   * thumbnail, and existing media items will use the current thumbnail, until
+   * the queue is processed and the updated thumbnail has been fetched.
+   * Otherwise, the new thumbnail will be fetched immediately.
    *
    * @param bool $from_queue
    *   Specifies whether the thumbnail is being fetched from the queue.
    *
-   * @return \Drupal\media\MediaInterface
+   * @return string
    *   The file URI for the thumbnail of the media item.
    *
    * @internal