I installed Battle.net launcher in Steam, the .exe file. From there I installed Diablo. Works fine. I had some performance issues and had to add some command line args. Codex/claude code helped me with all of that, it ended up running very smooth (I've since deleted it).

But Steam -> custom app -> battle.net exe -> run it in 'compatibility/proton mode' and you should be good.

Can't give you any specific help since you didn't specify your problems. However it worked for me in the steamdeck with Proton out of the box.

tl;dr: go to protondb.com, search for Diablo 4, and then filter the list of results by "Distro" for Ubuntu (and Mint), and try the options that people say worked for them

ProtonDB is a site that aggregates reports from users of Proton, the compatibility layer to let Windows games run on Linux. For lots of games, users will submit reports of their system info (distro, CPU, GPU, driver version, Proton version) and any configuration they needed to do to get that game working on their setup. The usual solutions are switching the Proton version you use and/or commands you add to the custom commands in the configuration for that particular game in the Steam menu.

I just looked at Diablo 4, and specifically filtered for Ubuntu users; I see 22 reports, with the most recent ones being people saying it worked for them. There are also successful reports from people on Linux Mint, which is based on Ubuntu.

Not sure. See if you shift the itch to another game, WoW I know works on Linux always. Diablo 4 in particular won’t even run on a Mac I believe, so they don’t care too much about making that multi platform.

Albion Online is another one with great great portability, literally on everything.