The common issue with Bluetooth Audio and mac OS
create an aggregate device via audio midi setup and do not include the your headset input channel in there, then make that device to be default.

that's an example setup, as long as you do not include your headphones input and use the build-in microphone, it should not trigger the SCO codec upon bluetooth initialisation. that generally means if you want to listen to music and talk it will use the laptop microphone, not the headset one.

hope that helps.