I have a very similar problem. I have an Uno, a Nano and a Nano Every and none of them will work correctly over the Serial.x commands in my Windows 11 PC. But it's not a total failure. Some of the Serial.print(), Serial.available() and Serial.parseInt() seem to work, but when there are several serial commands ,the unit will skip some of the commands, by not responding to Serial.parseInt in particular. All the units will work correctly with 2 computers that I have access to that are running Windows 10. So, for the moment, I have given up on the Windows 11 computer. I have tried new driver installation, but no luck. Hopefully someone will come up with a solution.