SteamOS is Valve’s Linux-based operating system. It features a seamless user experience optimized for gaming, while retaining access to the power and flexibility of a PC, and plays tens of thousands of games on Steam. SteamOS officially ships on Steam Deck, and will soon ship with certain Legion Go S models. We’re currently working on adding support for more devices.
afaik yes, you just have to install Steam and Enable Steam Play. There’s also Lutris which includes support for Steam and other stores.