Got my 21 ultra four days ago. Came from a Note 9. I have a Motorola headset on most of the day. Never had an issue with a disconnect with my Note 9.
About maybe every 1-2 hours I get a notification through my headset that the Bluetooth has disconnected and reconnects fairly quick after. That happens when I'm not on a call.
When I'm on a call it doesn't alert me but I can tell I lose the person I am talking with for about 5-10 seconds.
I have done all the clearing cache, resetting network, etc. Was hoping someone might be able to give me any tips.
have you tried it in safe mode? try unpairing the BT device and pair them again
or submit an error report via samsung members app when it disconnects again (members app > + button > error report)