Meanwhile I play all my GOG games on my SteamDeck. Sure it runs SteamOS and Steam in a sort of Big Picture Mode, but it’s still just a Linux PC, you’re free to use whatever software on there in Desktop mode, and then you can add all the apps and games you want to the Steam launcher, and run them that way. You’re not forced to stay in Steam, nor are you forced to only buy games from Steam. You can exit Steam on the Desktop mode and still use Proton to play Windows games, but that leaves you with more overhead running than when you do it from Steam in the big picture mode.
Meanwhile I play all my GOG games on my SteamDeck. Sure it runs SteamOS and Steam in a sort of Big Picture Mode, but it’s still just a Linux PC, you’re free to use whatever software on there in Desktop mode, and then you can add all the apps and games you want to the Steam launcher, and run them that way. You’re not forced to stay in Steam, nor are you forced to only buy games from Steam. You can exit Steam on the Desktop mode and still use Proton to play Windows games, but that leaves you with more overhead running than when you do it from Steam in the big picture mode.