It's been a rollercoaster day trying to get the Diablo IV Beta running on Steam Deck, but thanks to the awesome community, we managed to get it up and running and tested
You will need GE-Proton7-27 to play Diablo 4 on Steam Deck through the battle.net launcher
You will still get an error about the graphics card being unsupported but just ok and you will be into the game
You will also need the UMA Buffer Fix which we have covered previously here
And if you haven't installed Battle.Net on your Steam Deck yet, then we have a guide for that too here
If you need help with installing GE-Proton versions, you can check out our guide for that here