I had Diablo 4, the Battle.net version, running perfectly fine under Lutris Flatpak. Then randomly one day it just stopped working, I didn't download a new version of the wine runner I was using, I didn't make any configuration changes it just broke. Specifically it boots, the screen goes grey for a few seconds, and then it loads up super slowly, like 1 fps and makes the game interface and Plasma becomes unusable, so I have to drop to a TTY to kill the process. Nothing really interesting is show if I select "show logs" in Lutris.
I was thinking some Flatpak Lutris update broke it, so I tried to install the game using Bottles, also a Flatpak, but ended up with exact same problem. Now I am thinking this may be a Mesa problem since that is a dependency both of these Flatpaks share. I am using the same Wine GE version on both, but it's a version from February and it worked just fine a few weeks ago.
Any recommendations on what I could do or what I could look at to debug further?
Yes caffe is a runner in bottles. Try it to see if it works for the game. Bethesda BattleNet Launcher works with it.
Make sure to update the distro if possible.
Sometimes restarting the device if you never do, might help in certain scenarios. Some updates need a restart even though most don't on Linux.
EDIT:
You can try running the Battlenet launcher on lutris and running diablo 4 through instead of standalone. Blizzard launcher sometimes with updates breaks the launching on lutris. It's why I suggest to try caffe on bottles. Download the .exe for the battlenet launcher and install it on bottles with caffe runner and run it there. Hopefully some of this might fix it. Or someone that has used Suse with more experience might suggest what to do. I don't have that game but these suggestions are based on my problems with Battlenet launcher for the last year.