Depends on the game’s anticheat. ProtonDB is a site that tracks Steam Deck (and Linux in general) support for games. You can check what you play to see if it would run on Linux with Proton, the tool Steam uses to run Windows games on Linux. If you want a desktop similar to SteamOS, any distro that supports KDE Plasma will have the same desktop as SteamOS’ desktop mode, with the new Big Picture Mode on Steam being the Steam Deck’s game mode