Are you using Bookworm? I had trouble getting sddm on it to use system resolution. Normally I would ignore that but I only installed it on a VM so I could record an intro for my stream of Debian booting into the gaming.
I haven't updated my machine yet because I have no experience with wayland or pipewire and Nvidia with gaming. I was also interested if it's pretty decent with games and nvidia yet.
I am. SDDM should work properly out of the box, maybe it's a wierd issue with virtualization?
Wayland is pretty much plug and play if you install xwayland (with the exception of OBS studio which used to be wierd about Wayland surfaces, I think that's fixed now). Pipe wire has been working fine for me.
Yes, I thought it might be a weird sddm bug so I installed gdm and configured that too with the same result. Next option is to try a different distribution.