From my experience some machines/systems will run the game correctly with Proton Experimental while some will launch it only using Proton 7 or Proton 9.
I haven't checked if it runs on Hotfix, but feel free to try it if you want.

If this guide doesn't work with the version you selected, you might need to change Proton version, run the game at least once on changed version and reapply the steps below.

1. Run the game at least once so Proton configuration would be created.
   
2. Install Protontricks. You can install it by typing the line below into the terminal:
   
   flatpak install com.github.Matoking.protontricks
3. Use Protontricks to edit game's Proton configuration.
   
   flatpak run com.github.Matoking.protontricks
4. Select FreakOut: Extreme Freeride >> Use default Proton prefix >> winecfg >> Libraries
   If you see a number of popup windows after selecting the game, just click Ok on each of them.
   
5. Type in these entries and add them to the list:
   
   msvcp71 msvcr71 d3dx9_29 d3dx9_30
   
   
6. Confirm with Apply and exit configuration by choosing Ok and then Cancel each time a new window pops up.

1. Make sure config.cfg file is present in the game's directory.
   If not, create one and paste in the lines below:
   
   
   width 1280 height 720 bitdepth 32 usesound 1 window 0 widescreen 1 framesync 0
   
   
2. To make playing in fullscreen possible, you need to remove or rename two intro clip files in the FreakOut Extreme Freeride/Data/Common directory:
   
   Coldwood.wmv JoWooD.wmv
   
   Rename them to anything. Personally I add .bak at the end of these file's names.
   
   
3. Once it's done the game should start and all you need to do is to skip the intro by pressing Enter.
   
   
4. If you're playing on Steam Deck, you might want to setup additional key bindings to skip the intro, properly navigate through menus and move around in the game.

At this point the game should display the language selection menu.

Once you select the language and profile, you will be able to adjust the window resolution to fit your display from the Options menu.

Hope this helped! ;)