For VRR, using Plasma on Wayland seems to work just fine for me (after you enable it), as long as the game in question is in full screen; it doesn’t seem to trigger otherwise. I think I ran a mixed refresh rates setup once too (165hz and 60hz) and didn’t have any issues. Idk how X11 handles mixed refresh rates (if at all), but it definitely didn’t support VRR well if at all when I tried.
Re: HDR, yeah. Color management is also missing in Wayland (but present on X11) iirc.
(In case you didn’t know, there’s currently two display “servers”/protocols that are in popular use, X11 and Wayland. X11 is old and has screen tearing issues, but greater support in general. Wayland is newer and has far more isolation between programs, and aims to replace it (and Fedora already has made it default, iirc))
it supports it through jitsi meet i think for group chats, but 1 on 1 it seems to do something different, though it’s been a while since I tested (this is all in Element, btw)