This game used to have a native linux build as a beta, but since Steam doesn't really have any way to specify a game as only supporting a platform as beta, the developer pulled the linux builds. You may need to force the use of Proton in the title properties depending on when you purchased the game.

Proton works like a charm though. Just a note - this game is remarkably demanding by default, even on windows. If you experience a ton of lag on low end machines, lower the vfx settings.