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.
Oh, cool! I had no idea this was a shared universe thing that others were contributing to. Looks like there’s yet another fan project called Ashes: Epoch, a prequel to the first game.
Man, tons of great stuff going on with that world.