I have the same problem with Big Sur on an iMac (Retina 5K, 27" 2019). No solution so far. It's happening a LOT. No bad memory. Attempted with connected devices, etc but no solution.

I'm only on the Public Beta 3 and same thing happened to me. No bluetooth, no volume, no displays, no date/time in the menu bar... third party apps show up, as do Spotlight and Siri but that's it. What a bummer. This needs to be fixed ASAP. 11.3 Beta (20E5210c), iMac Retina 5K 27-inch, 2019 (I've reset PRAM, ran Disk Utility, changed all the System Prefs including Control Center, etc but nothing brings it back)