Specifically, I have a 49" ultrawide monitor and a VM in it. If I share the entire VM, other people with smaller monitors see it too small and have to zoom. If I resize the VM, I have to reposition my windows inside it.

It's easier to share a portion of the screen, it's what I do in Zoom. A portion of a window would work too.

Max here from CoScreen. I'm with you, sharing a portion of the screen or window would be very useful for this scenario. I can also imagine running CoScreen from the VM itself, but that would only work for Mac and Windows VMs at this point (Audio and video could still go through your physical machine —— i.e. you would connect with two users). We also have a headless Linux client in the pipeline that could serve to connect the VM directly.

Connecting with 2 users would work. I would still need to resize the window I'm sharing (the reason I have that big ass monitor is to use VS maximized and have everything open), but it's easier than resizing all windows.

I do that all the time in Zoom, to share PowerPoint presentations without exposing the speaker notes on my main screen, and YouTube videos from Firefox (just the video portion, not the "chrome" around it).

Fascinating, thanks for the detailed context. We'll look into it!