You don’t need to use steamtinkerlaunch, putting gamescope --hdr-enabled --fullscreen -W width -H height -- %command%
into the launch options is enough.
Will the Gnome version of Bazzite work for HDR on an Nvidia GPU, or for that matter any other OS as long as I’m using gamescope to run the game with HDR enabled?
Gamescope can’t make a different compositor support HDR. Until Gnome supports HDR and the protocol used by gamescope, it won’t work.
Xwayland doesn’t get input in some special way, it uses the exact same Wayland protocols to get input events as native Wayland apps. All claims about it being more complete or anything like that are nonsense.
Krita forces Xwayland because they have some X11 specific code they haven’t bothered porting away from, that’s all.