Another Linux user here (Pop!_OS). Did you manage to get this to work via Proton? I followed the tutorial for installing via Melon Loader, and everything seemed to go as intended except for that when I launch the game, I don't see any sort of terminal window for Melon Loader (like you described). I tried to follow some guide online for launching games via Proton, but I couldn't actually get the game to launch with this method.