Welcome to the SteamDeck Bay! Located on this site are guides on how to pirate, how to download .exe files and more of the sort. Enjoy your stay matey!
On desktop mode, navigate to the discovery store and download "Heroic." Once you have it downloaded you can go into steam and add it as a non steam game. As you launch it you'll now have access to the epic games/gog/prime stores and from then on you can buy/download games from the store and launch them from there in gaming mode.
On desktop mode, go to the discovery store and download "Prism Launcher." Once it's downloaded, add it as a non steam game. Once you launch it you can select what version of MC you want to play, and all kinds of mods. (If anyone wants a more in depth guide on how to mod and whatnot, let me know.)