>>527682332
Holy crap, thank you for pointing this out. To be honest, I never heard of Adventure Game Studio and hadn't even bothered to check what engine Kathy Rain uses, so I just had no idea that I had the option to run it natively. (I did see that the Director's Cut version has a Linux version available directly through Steam, but SteamDB says it uses Unity Engine.)
I was about to ask how to run Kathy Rain through a native build of AGS, but it looks like AGS is built into ScummVM — the compatibility page on the ScummVM site lists Kathy Rain as compatible — and I already have ScummVM installed. And now I see the game is even supported by GameDataPackager, so I could use that to install the game as a system package with ScummVM as a dependency. (Not that there's any real point in doing that, except for fun; I already installed Phantasmagoria and a few other games that way.)
As much as I prefer to run games natively, though, I might just finish out my first play-through in Proton for the achievements now that I've already gotten half of them, unless native AGS can be dropped in without breaking Steam integration.