Multiple people have been reporting that their Moodle installations don't show updates anymore, see e.g.:

https://moodle.org/mod/forum/discuss.php?d=449555

https://moodle.org/mod/forum/discuss.php?d=450345

After some testing, it seems that the problem lies in the Updates API provided by download.moodle.org.

The following link demonstrates the problem:

https://download.moodle.org/api/1.3/updates.php?branch=4.1&version=2022112801.00

Expected result: A response with an updates array containing available core updates.

Actual result: A response with an empty updates array.