When using a Macbook Air M1, the game always starts in a window. That in itself is not a problem. If you change the window size to an unusual ratio, everything will be neatly rearranged. So far so good!!
You can also see the incorrect aspect ratio on uploads to your Zwift account / Strava.
For what it’s worth, I use the settings below, but changing them doesn’t solve anything:
Game resolution: 4K UHD 2160p
Screen Mode: Full Screen (what does this option do, it makes no difference on macOS)
I’ve spoken with Zwift support about this issue and been back and forth with screen grabs and details so they are aware of the issue.
Its a real shame its not working 100% - as I use my ipad on the bike all wireless and its a neat solution - and having the improved graphics from the mac would be even better.
I looked at a usbc powered screen - but those are limited to 1m cable etc and not so slick.
Looks like this issue has been around a LONG time: