where to get games:
this will not probably work for most multiplayer games or always-online games like Genshin Impact
lots of games can be bought legally and DRM-free on GOG e.g. The Witcher, Baldurs Gate, Stronghold Crusaider HD
especially Indie Games can be bough and/or downloaded on itch.io e.g. Doki Doki Literature Club
there is always the option to pirate games
Lutris is a FOSS game launcher for GNU+Linux that handles installing from different (open-API) sources like GOG or itch.io or just a local installer file. It also manages wine/proton versions, settings and prefixes for each game. It also integrates with a lot of emulators for old consoles like 3DS, PSP or Atari.