We Can Now Easily Play Minecraft Splitscreen On The Steam Deck Thanks to a New Script
c/steamdeck · u/Fubarberry@sopuli.xyz · 55 points
It's using PolyMC to launch multiple instances (depending on how many connected controllers there are) and automatically tile them. I would personally suggest using an optimized minecraft build like Fabulously Optimized to minimize any performance hit from having that many players.