itch.io

Lookup wine-tkg or wine-ge-custom on github, there are scripts (and for some distros, prebuilt packages) that apply the proton patches to wine, that you can install systemwide to run anything.

I think you can also make Steam run non-steam games added to the library with Proton, but I haven’t tried that.

I play this game with Proton, it works well :) You can add non-Steam game into Steam. Come to our Discord if you need some help!

This (and a lot of other Punkcake titles) are getting Steam releases now, should be over the next couple of months.