Just looked it up, but it’s quite expensive compared to the <£12 I usually spend on steam games (eg Terraria, Stardew Valley, Portal)

Great, it was working without issues on Gentoo and Steam Deck respectively before, too.

I bought the Steam release day 1 and it has worked great with Proton. I played a couple forts and had my fill. Now that the Linux version is out I might have to run another fort on it and see how it works.