I think this is more of a Big Sur problem. On my 2019 i9 iMac I am getting very weird Bluetooth issues too. System Preferences is locking up for me (cannot disconnect any of the Bluetooth devices, right click is not working). I cannot turn off Bluetooth when it gets in this state. My headphones (5 year old Sennheiser Bluetooth) act up. I need to restart the entire computer. Everything was working flawlessly until Big Sur. No changes in wireless interference in years.