Disclaimer: The game doesn't run well at all, all the issues listed here are still present, the most annoying one being the constant stuttering of video and audio.

This seems to be caused by the game's poor use of multithreading and it maxing out a single core at nearly all times.

If all this doesn't deter you from trying anyways, here's how I managed to run Space Engineers from Steam using Proton:

proton-wine Edit: Proton 4.2 is based on Wine 4.2 so the following step is no longer necessary.

First of all you'll Wine 4.2 which is newer than the version shipped with Proton. Fortunately there's already an existing project called wine-proton for upgrading the built-in Wine and someone in one of the Github issues has figured out how to add this to the Proton version selection menu in Steam.

1. Create ~/.steam/steam/compatibilitytools.d/proton-wine and enter it.

2. Create compatibilitytool.vdf in that folder containing the following:

   "compatibilitytools"
   {
     "compat_tools"
     {
       "proton-localbuild" // Internal name of this tool
       {
         // Can register this tool with Steam in two ways:
         //
         // - The tool can be placed as a subdirectory in compatibilitytools.d, in which case this
         //   should be '.'
         //
         // - This manifest can be placed directly in compatibilitytools.d, in which case this should
         //   be the relative or absolute path to the tool's dist directory.
         "install_path" "."
   
         // For this template, we're going to substitute the display_name key in here, e.g.:
         "display_name" "Wine Proton"
   
         "from_oslist"  "windows"
         "to_oslist"    "linux"
       }
     }
   }
   

3. Copy Proton files from $STEAM_LIBRARY/steamapps/common/Proton 3.16 Beta/ into this directory. Replace $STEAM_LIBRARY with your default library's path.

4. Download wine-proton from here and unpack it over the existing Proton files in the current directory. i.e. dist/ should be merged into dist/.

.NET

Next we'll have to install .NET 4.7.2 using either winetricks or protontricks:

Edit: As pointed out by /u/Aberts10 this requires a winetricks version of 20181203 (where the dotnet472 verb was added) or later. Check which version is installed by running winetricks --version.

For the latter run protontricks 244850 dotnet472 and click through all the installers.

FAudio

The last thing we need is FAudio to fix ingame audio. Install it from Kron4ek/FAudio-Builds.

Now you can restart Steam, select "Wine Proton" for Space Engineers and start it. The intro video doesn't play for some reason so you'll have to press a LMB or ESC to skip the video and enter the menu once the game has loaded.

You may occasionally get a rundll32.exe warning but just answering it with "No" has worked fine for me.

Again, thanks to /u/LinuxDweller for doing most of the work needed to get to this point, your guides have been invaluable! I hope by writing this one someone more knowledgeable than me may be able to more easily debug the game and to work towards finally making it playable.