It's not an Apple issue. Works perfectly when you use a Mac + AirPods. The issue is when you try to use Windows. All bluetooth headphones I've tried (with microphones) sound horrible with Windows, if they work at all.
Airpods do not have better duplex audio on MacOS. The problem is that AAC cannot support high-quality recording and playback at 330kbps, so it has to degrade the quality of the recording stream to fit within the Bluetooth bandwidth. MacOS might default to using your laptop's microphone, but that's something you can also set up on Windows. Hell, it should be the default on Windows as long as you have AAC support installed - there's no reason a headset should be using SBC over Bluetooth unless the last version of Windows you used was XP.
I actually normally use my headphones through my phone, but I doubt ios is doing anything differently compared to macos.
The point isn't that there's only so much bandwidth for mic + headphones, the point is that the bluetooth stack on Windows just doesn't work. I tried connecting multiple bluetooth headphones (Airpods, Beats, Sony) to a new Windows 11 computer (Microsoft Surface). I only got one set paired and it defaulted to the headset profile immediately. It was horrible. The others never connected or the connection was unreliable.
The process was so bad, my son recently bought a set of wired headphones just to avoid the entire issue.
If you've never been in the Apple garden and used headphones + device, it's a night and day difference in experience.
I haven't used Windows in years, it's a pretty bad point-of-reference for me. However, I can say pretty confidently that iOS, Android and Linux all have more reliable Bluetooth stacks than MacOS. In fact, the stack on Linux is so good that I don't lust for Airpods at all. I just turn on my Sony XM4s and it automatically connects to all my devices. No muss, no fuss.
Oh, and neither MacOS or iOS support high-bitrate audio playback. They're not even on the same eschelon as Android or Linux, which support codecs like LDAC and APTx, with 3x the bandwidth of Apple's 330kbps AAC stream. Come to think of it, if Apple switched to APTx for their newer Airpods, they would have no problem recording and playing audio back at the same time.
All bluetooth devices do this on all platforms when you use both sound + microphone. It has to split the available bandwidth between the two.
My Sony headphones will go into "headset mode" on Windows and Mac and sounds horrible in both, just have to make sure no programs are trying to use the headphones' microphone and then you get full bandwidth for audio.
