this is fascinating..
Is it possible to install Arch linux and add the SteamOS layer and cut over and back again as desired?
You can also just go to the normal KDE Plasma environment from the steam menu and use it like normal Linux - or even install let's say emulators from Arch repos and add them to Steam then run them from SteamOS interface.
I've only run SteamOS on my Deck, but afaik if you install it on something else then you can still flip it between the gaming mode and the desktop mode. In desktop mode it behaves exactly like you'd expect an Arch Linux install to behave, and you can mess around with it as much as you'd like. In gaming mode it's like a console and really only plays games (but isn't limited to Steam games - people have got it running emulators and all sorts of other stuff too).
There are a couple of other game launchers, like Heroic, which handles both Epic and GOG games, which also works great.
But what's even better, is that if a GOG game doesn't quite run perfectly on Heroic because it lacks some of the latest refinements from Proton, you can import that game into Steam and taie advantage of Valve's nice work on Proton anyway.
I might do that; Cyberpunk on Heroic doesn't support raytracing or DLSS, and as I understand it, those do work if I were to run it on Steam. So that's a very nice option to have.