[chris-orgmenta]

Ah that's cleaner than my idea. Which was:

Install OBS, add a 'Scene', add a 'Window Capture' to the scene, then right click it (in sources) and transform / scale / crop the scene dimensions. Then optionally in the 'controls' panel you can start a virtual webcam, then go to Chrome/Brave settings, go to Site & Shield settings, set the default Camera to your virtual one.

Not sure if OBS would solve your Mac issue.

[rcarmo]

It wouldn’t really, since I don’t want to replace my camera feed—I just want sharing to share a region of the screen, like you do.