Changing bluetooth audio codec

I disagree. This is not an issue with Bluetooth or compatibility. The headphones are compatible and Bluetooth is working as it should. This issue lies entirely with Fairphone OS. It is a bug, plain and simple.

This issue appears fixed for me with Android 11, at least with AAC (Bose Quiet Comfort 45).

Probably not. If you read carefully, you’ll learn that the described problem has not occured with Bose, moreover it is stated, that Bose seems a bit of an exception as headphones of other manufactorers simply do not work.

Actually, the issue IS fixed as of now! At least for me on my FP3+ with my Sony WH-1000XM4 headset: