Read my post here:I'm going to be crazy...
I have 2 Mac Pro 5.1 (mine is mid 2010 dual Xeon, and my wife's one, a late 2012, mono Xeon). Both with Big Sur and OC 0.6.7.
My Mac Pro goes perfect, without isues... but the other... the other will meke me crazy!! Some times, in a cold boot don't recognize the mouse or bluetooth... other times, when power up after hibernate, don't recognize the mouse or bluetooth... and other times, random, without hibernate, writing an email for example, the same trouble...
The bluetooth it's a USB dongle attached to the Apple's keyboard (the usb dongle it's ok, it's the third with the same issue). I was try to attach this dongle to the front and rear USBs directly... and the same issue...
It's like if all USB turn off, becouse the keyboard (I test with 2 keyboards) don't work too when the issue (for example, I press Caps Lock and don't brigth the led).
If I disconnect and connect again the keyboard, all will work again in 5-10 seconds...
Do you know what can be???

OpenCore Big Sur: Random loss of Bluetooth functionality
20210315 Edit: There are two distinct causes for BT loss with Big Sur: Multiple bluetoothActiveControllerInfo inside the NVRAM main VSS store that cause conflict and the real BT controller to be ignored at POST. Poor legacy USB support with Big Sur, MP5,1 bluetooth controller is a USB2.0...