Valve has recently launched a tool that allows you to check what games from your Steam library have been tested and confirmed to work with the Steam Deck. The Steam Deck runs the custom SteamOS Linux distribution with the Proton compatibility layer for Windows exclusive titles. The compatibility tool from Valve lists games that have been tested into three categories consisting of verified, playable, unsupported in addition to a list of currently untested titles. Valve classifies games listed as verified as not needing any configuration for use with the Steam Deck and those classed as playable may require modifications to get controls working correctly. You can check what games are supported from your Steam library by following this link.