[felurx]

This was quite an annoyance for me too. I discovered/noticed two things, but I'm on Manjaro, so YMMV: Whether A2DP or HFP is used can be controlled by changing the profile (or whatever it's called) of the audio device, in the audio settings. Take a look in the settings where you can change volume per app and all that good stuff, and try to see if there's some dropdown that lets you pick between Headset and Headphone, and all that.

Second thing: The actual default behaviour seems to be to use the profile that was used last time. But for me, whenever MS Teams is running, it decides that the correct thing is to switch it to Headset mode, because Microsoft knows what you want better than you do, and you want the option that produces shitty sound quality, but bidirectional audio.