personally as far as handheld PCs go i think linux/steamos edges the competition, at least as far as the UI goes, all the other handhelds use windows and use a barely functional "quick access" menu, the steamos one isn't perfect but it's much better than the horror stories i've heard of the stuff like what's on the asus rog ally and msi claw. i know windows has big picture mode but it has to run on top of normal windows explorer which isn't ideal, and the quick access menu doesn't have everything like screen refresh rate options
you don't have easy access to games with anticheat protections but i feel like complaining about that is moot if you're using a handheld device that likely won't have 100% access internet at all times