Hi, fellow linux user here:
- download the demo and extract the zip
- open Steam and in the bottom left corner go to "Add Game" -> "Add Non-Steam Game"
- choose the "Silverfish.exe"
- Now in your Steam library right clock the new "Silverfish.exe" entry and go to "Compatibility" and tick "Force the use of a specific Steam Play tool"
- in the new dropdown choose "Proton experimental"
- launche the game and enjoy, games runs flawlessly so far for me on linux, as did ADACA before it