I manage to get the battle.net launcher to launch and work through steam with cachyOS proton. If I ever get a steam deck, I might see if the custom proton version makes any noticeable difference on it.
I've been grinding diablo 2 resurrected with it, getting a stable 144 fps. Definitely like it more than using windows 11.
I also managed to get steam on cachyOS to read my games on my windows nvme drive. The whole point being I wanted to try Baldur's gate 3 on it without having to reinstall over 100gb. That said, I was having freezing issues and low 1% when playing on windows. It was becoming borderline unplayable. However on linux I have none of these issues. Game works perfectly fine, granted after fixing some controller issues.