[tempaccount420]

What I'd like to know is if there's still a bandwidth issue, where if you use the microphone, the audio quality downgrades severely.

[Gigachad]

That's because old bluetooth has two main modes A2DP which supports one direction high quality audio and HFP which supports microphones but sounds like shit. Bluetooth LE Audio is fairly new and supports high quality audio and mic at the same time. But as far as I'm aware, no Apple product supports it yet.