As previously reported, the game works with Proton 3.7-8 after some setup. These steps require both wine and winetricks to be installed in the system. (1) Before initially starting the game (no prefix created yet), rename /.steam/steam/steamapps/common/Steamworks\ Shared/_CommonRedist/DotNet/4.5.2/installscript.vdf to prevent Steam from installing .NET in the new prefix. If the prefix has already been created, delete it: rm -rf ~/.steam/steam/steamapps/compatdata/345390/pfx (2) Press Play to get Steam to create the game prefix. The game will not actually load yet. (3) export WINEPREFIX=/.steam/steam/steamapps/compatdata/345390/pfx (4) Run 'wine uninstaller' and uninstall wine mono (5) Install dotnet40 and xact using winetricks (6) (Optional) Rename the file from step 1 back to its original name (installscript.vdf).

The first time I started the game after following these steps, Steam threw out a couple errors about not being able to find a proper runtime for the executable. The game started up anyway, and subsequent startups have not given that error.