It would appear this is going to be one of those issues that a) just silently goes away in a future update OR b)when we've all given up and bought M1s.

Same issue, I suspect external monitors. As someone pointed out, no problem with Win 10 in forever. This is my first Mac, I have no delusions about stability, it immediately trashed my exfat RAID. This is the third version of the OS. Apple Support: Did you reboot? Not impressed.