Your AirPods may be comfortable with great noise-cancelling for when you want to block out the outside word; as well as fantastic "transparency" for when you want to still hear it. The audio quality however is sometimes just terrible.
This isn’t to say it’s always terrible, in fact it is mostly surprisingly good.
When on calls however and using the AirPods as both microphones and headphones, the audio quality is greatly reduced.
The Quick Solution
In macOS simply select a separate microphone.
"Option (or Alt) ⌥ + Click" on the sound icon in the menu bar, and then select an alternative microphone.
If you don’t have the volume/audio button in your menu bar you can also do this easily from sound system-preferences:
I’ve found that using my laptop’s built in microphone works well and others are able to hear me as long as I don’t have too much background noise.
My AirPods, providing output only, now offer much higher audio-quality while on calls.
More details on changing input device here: https://support.apple.com/en-gb/guide/mac-help/mchlp2567/mac