Have you tried CTRL + K (Windows)? It’s Oculus’ Build and Run feature which is much faster than using Unity’s Build, although I highly doubt it will help.
Also try searching the forums, there are quite a few people who have had this error, even this person said “there were lots of solutions online on this topic” - and they found yet another solution (do a factory reset on your headset):
Otherwise it might be a Unity bug if it’s working on 2020 and not 2021, you may need to file a bug report.