I've been testing CiviCRM 5.57.4 and noticed that I can no longer type in the Case ID when searching for the case to file an activity to. (I'm in Drupal 7) In version 5.45.7 it was still working. I verified that on dmaster it also does not work - I did create a case or two to test with since the sample data doesn't include cases.
I don't see any changes to the core file Case/Form/ActivityToCase.php that jump out at me as the cause. Does anyone know where else I could take a peek?