Im having the same issue. I tried MANY things today with no luck and actually fear I messed things up on my install since I did so many things!
I tried guides like: 3rd Party Bluetooth Binding. Beta testers needed and reelyActive Smart Spaces Revisited but all lead to dead-ends with the bluetooth device never showing up in the inbox and errors in the openhab logs.
Any help would be appreciated (BTW I have a Raspberry Pi 4 and am trying to use the builtin bluetooth, with openhab 2.5.2)