ReadOnlyUser
If I understand correctly, the other OP describes exactly your problem with Bluetooth on incoming calls:
I have pixel 6a and pixel 7 with latest Graphene and the incoming calls do not work on Bluetooth headset for the added User configuration. The owner config Bluetooth headset works well.
I can also confirm exactly this bug: In the owner profile I can accept incoming calls via Bluetooth and make outgoing calls.
In other user profiles, I can make calls via Bluetooth, but when I receive a call, I cannot accept it via Bluetooth.
My not very sexy but working workaround: Don't answer the call and call back immediately - than you can use the Bluetooth headset as desired.