I'm experiencing the same thing with my MBA 2020, but I figured out a small fix for Zoom calls.
The video quality seems to be worse for Zoom calls because the system (Apple? Zoom?) automatically zooms in the picture, usually so that the top of my head is cut off when I am sitting right in front of my MBA. I couldn't figure out a way to fix this by changing the settings, but this seemed to do the trick:
Begin video call on Zoom (video will be zoomed in)
Open Photo Booth
Video magically zooms back out to normal on Zoom!
You can then close Photo Booth, but it seems like changing any video settings on Zoom will send it back to default (zoomed in).
Does this trick work for anyone else? Do others think that the camera quality is worse on Zoom vs other programs?