I really do not think new user experience should be "go read the entire documentation" when you have "new user guide"[1] that does not mention any of this. The closest to it is the "oh btw there is also game mode docs here" - guess what, still doesn't explain that you're not getting linux experience when you install this linux image.
delete 2 files from /etc/sddm.conf.d/etc/sddm.conf.d(1 file if you want to have a touch keyboard for login) build image boom you got an SDDM login screen and get to keep gamemode (except "return to gamemode" and "switch to desktop" just logs you out now)
why do we not provide this? it is an unsupported configuration and it is not worth our time to maintain an image to just remove 2 files for you.