The most common cause is an incompatible driver installed during the update process.
After messing around for an hour, I finally fixed it. Here is what worked for me in case anyone else is panicking: after update to windows 11 keyboard not working
If you are reading this on your phone because your PC keyboard is dead after the 24H2 or 23H2 update, take a deep breath. You are not alone. This is one of the most frustrating post-update bugs, but in 90% of cases, it is a hardware failure. The most common cause is an incompatible driver