The Standalone release is Windows only, but I can confirm it works just fine with Proton in steam after adding it as a non-steam game.
Alternatively, you can download the .Pk3 version, which allows you to run it natively through the Linux version of GZDoom.
Really recommend giving it a try, it’s a fantastic little game with a lot of effort put into it. The gunplay feels great, the environments and art are awesome, and the level design is solid.
I noticed it there, but it seems like on the GOG page it says it requires Doom II to function, so I opted not to link to them since it wouldn’t be free then. Do you happen to know if it works without any tinkering for GOG users who don’t own Doom II?