I heard with our resident Steam OS user, who said the Itch version works for him, and that it should for you too if you:
- Install Windows version of D2 through itch, preferably launcher
- Add Game.exe to steam with right click
- In steam in gaming mode, open the game properties for Game.exe and under compatibility force use of Proton, any recent version should work
- Run the game through Steam
Hope this helps!