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.
Once you've downloaded the games files, it will be a .rar zip. Go to dolphin and create a new folder and give it the name of the game you just downloaded. Now take the zip and extract it into that folder. Locate the exe file in that folder and right click to add it to steam. Now you're basically done! The last thing you need to do is go on steam and go to the properties of the game and figure out which proton version works for the game. Most older games will work with proton 7.0.6, and newer ones usually work with 10-24, it just depends.