Are you passing through a GPU? If so, are you sure the proxmox host isn’t using it?
Edit: Just saw the link in the post was to a GPU passthrough guide, so better question, do you see the GPU from within the VM?
I’ve admittedly never tried gaming on a linux VM or LXC in proxmox, but I’ve done other tasks that required GPU hardware acceleration with no issues with both.
I’ve only played the demo for this one (and liked it), but the first one is amazing, and there’s a good chance this will be my favorite series of games ever if they continue to make them. Very excited to play this.