2020 5K iMac shows persistent Bluetooth connection requests

My 2020 5K iMac running Tahoe has just started insisting on a Bluetooth connection request.

It does stop when I turn BT off entirely, but otherwise it goes away and comes back less than a minute later whether I click ignore or cancel.

It doesn’t seem to actually accept “ignore” because the box never gets checked. I’d expect to check that and still have to “cancel”. I also find it odd that a passcode would be simply “0”.