This is an interesting topic for a hearing aid user like me. For FaceTime and other calls on my computer or iPad/iPhone, I always physically switch from my Bluetooth hearing aids to AirPods, since the hearing aid microphone isn't that good for calls (other party has problems hearing what I say). Now, this could be a bandwidth issue. Apple Audio MIDI Setup shows the hearing aid microphone as an 8kHz/16bit mono input device, while the output is 2 channel 32-bit Float 44.1 kHz.

The switching is a bit of a hassle, since I have to remove and turn off my hearing aids (which I would only do in private anyway), before putting in the AirPods. And the reverse, after the call has ended.

Therefore, it would be very convenient if I could just switch to better input microphones, like the MacBook's. I'll give this a try.

If anyone knows if this is also possible on iOS, please leave a comment.

Edit: Thanks to other comments I've learned, that switching to another microphone is built into macOS.