Recently my bluetooth headset starts to act up when listening to music from MacOS. I initially thought it has died. Turns out it is an OS problem.
Basically if i use it as both input and output device, the sound quality is awful. So one solution is go to the
sound setting and manually select input device
internal microphone. Then looks like the audio will be back. However if you re-connect the device, it defaults to the bluetooth device as input again. quite annoying.
Another possible solution I found is to adjust the setting from the
bluetooth explorer which can be downloaded from the Apple developer site‘s
Hardware IO Tools for Xcode section. The downloaded the
dmg is a bundle of various debugging tools. Open
Bluetooth Explorer and go to
Tools -> Audio Options -> force use aptX, and check the box. This will also improve the sound quality.