Disclaimer: This is an unofficial way to run the game and in no ways supported by Egosoft. It is meant as an interim solution until there's an official Linux build. While it generally does work really well, please do NOT report any issues that only arise as a result of running the game through Proton to Egosoft, but only in this thread.
Limitations:
- Joystick twist doesn't work
- some sector music is slightly sped up or slowed down (happens rarely)
- you'll be unable to play the native version of X3TC and X3AP through Steam. If you want to keep playing these versions, please make a backup of your X3 Terran Conflict folder before proceeding
- Quitting the game won't quit all processes and you're forced to forcequit the game through Steam
- X3: Farnham's legacy
- protontricks (you may also use WINEPREFIX and winetricks if you know what you're doing)
- a custom version of Proton (whether the custom Proton is actually needed hasn't been tested. I just tested it on Proton 6.1-GE2)
- Make sure "Enable Steam Play for all other titles" is enabled in your Steam settings
- For X3TC, X3AP and X3FL, go into the game's properties, go to the compatibility tab and force it to run through Proton 6.1-GE2 and let them update or install them if they're not already installed
- Run X3FL once. You'll notice missing sounds
- Navigate to /path/to/steamlibrary/steamapps/compatdata/483330/pfx/drive_c/windows and delete system32/gdiplus.dll and syswow64/gdiplus.dll (these are symlinks to the version supplied by Proton and having these symlinks there will cause protontricks to fail)
- open up a terminal and run: protontricks 483330 wmp11 devenum
- run the game once. Videos will now either not work or have no sound
- back in the terminal, run: protontricks 483330 quartz
- launch the game again and things will be broken
- back in the terminal, run: protontricks 483330 amstream
- launch the game and enjoy X3FL