Xorg works fine with VRR on a single display although no one should use Xorg, it's legacy software and no longer in development.
Wayland VRR works out of the box with most popular DEs like KDE or Gnome.
HDR can be added to gamescope, but be aware it's still considered experimental.
AMD experience was nothing but flawless, only Nvidia was buggy due to their drivers, but they're preparing Wayland support soon.