That description is pretty hyperbolic. The SteamOS UI (eg. the Steam Deck-looking part) is very broken on Nvidia right now, but the actual gaming part (eg Proton and the Steam launcher) works fine. If you just want to play mouse-and-keyboard in desktop mode, recent Nvidia cards are generally pretty cooperative.
Well, I'm not smart enough to know if it's hyperbolic but it's a pretty damning statement right there in the README. Certainly enough to turn me away from ever trying it on one of my machines.
