Sorry, re-opening as it could still be an issue in D10, so changing to that version.
Closing as this class was removed here https://git.drupalcode.org/project/drupal/-/commit/360a9c5855084aaf1dce4... as part of removing update hooks added prior to Drupal 10.3.
Looks like the fix will come with https://www.drupal.org/project/drupal/issues/3043725 ✨ Provide a Entity Handler for user cancelation Needs work which is a generic solution, so marking this one as duplicate.
(Also found there was a similar issue for D9 and a fix which makes the media item anon when saving if it doesn't have an extant author: https://www.drupal.org/project/drupal/issues/3057004 → . That still works for 11.)