Linux version is just an empty folder. With Proton it works without any issues.
No issues
Native Linux version is not full available. Force a proton version.
Native version doesn't work, or rather, it doesn't exist. On Proton it runs fine but it hanged on loading screens a few times.
Finished the game without issues. Need to manually force proton since there is an empty linux depot but that's not really proton related.
I had to "Force the use of a specific Steam play compatibility tool" (a new Steam beta feature) in the game properties since the game has a broken Linux repository. After doing that, the game is downloaded and installed and works perfectly.
The developer has already added an empty Linux repository, they mentioned in Steam forums that a Linux version is coming. Because of that repository, the windows version cannot be downloaded and since the Linux repository is simply empty, the game is currently not playable in Proton.