The new Diablo works perfectly in Wine/Proton. Battle.NET has a chance to need some tinkering, but works. In case, there is an automated script to install multiple 3rd party launchers in Steam via Proton meant for the Steam Deck, but of course there is no reason they won’t work on a desktop Linux.
I don’t own Diablo, but I had to setup Battle.NET to install Heroes of the Storm. Can say there wasn’t much to talk about.