You will need a key to activate FUEL when you launch it the fist time. This key is your personal game key that came with your Steam copy of FUEL. You can find it in the game's context menu in Manage -> CD keys, you can copy it from there.

The first launch will take you into the game config tool. Go ahead and make any changes you want. You will have to use the "mouse" for this (STEAM+right touch pad).

The resolution should already be correct, but you can up the video settings. The Steam Deck can handle it.

Once you are done, press play, which will likely take you to...

The first time you try to launch the game (after the setup) you will be prompted to activate your game. The key that you need to enter here is the key that you copied in the first section of this guide. Paste or enter this key here and it should unlock.

At this point, if you launch FUEL it will just be stuck loading. Exit the game from the Steam menu, it's time to go to...


At this point I'm going to refer to Lucis Caelum's excellent guide:
https://cs2bus.com/sharedfiles/filedetails/?id=268031297
What you need is the files linked in there, and just like the guide suggest you have to copy those files into the game directory. This is no different for the Steam Deck, except you will be doing it in Steam OS Desktop mode. You should have no problems opening the rar file. Use Desktop Mode Steam to open the FUEL installation folder and copy the .dll and the .ini files right in there.

If you like you can edit the .ini file to change your user name. If you have an old save game you want this name to be the name of the folder inside the "My Games\FUEL" folder.

While you have the FUEL installation directory open, once you are done configuring FUEL for your Steam Deck, you might as well disable the launcher. (Hint: At this point you can launch FUEL from the desktop mode Steam just fine, you don't have to switch)

In the FUEL folder:
- rename GameSetup.exe to GameSetup.original.exe (or whatever you fancy)
- copy the file SecuLauncher.exe and paste it back into the same folder. Instead of overwriting, rename it to GameSetup.exe.

If you ever want to have the launcher back, rename GameSetup.exe to GameSetup.launch.exe and rename GameSetup.original.exe back to GameSetup.exe.

Credits:
https://cs2bus.com/sharedfiles/filedetails/?id=122307904

That's it, FUEL should now launch into the game without a launcher and work just fine, including saving.

Have fun!

Just in case you are wondering, the save game location on the Steam Deck is:
I have not been able to make my old save game work though. Leave a message if you managed to do it! 😊