Is it that to fire the guns you have to push the right thumbstick in?

If so it is an issue with steam controller support settings interfering with the xbox controller.
I have it working normally if I have steam controller support for xbox controllers off globally:
Go to steam in the top left of your steam window
Click "settings" in the drop down
Click on "controller" on the left
Turn off "Enable Steam Input for Xbox Controllers"
Then go to the game in your library
Right click on it and go to "properties" in the pop up
Click on "controller"
Select "Enable Steam Input"

Your controller should now work normally.
If not you could try combinations of on or off globally and then off, on or default for the game.
I swear each time they update the controller support I have to find out which combination works. Though this seems to work for both this and Commanche 4 which was another one that suffered.

Yes, that's exactly it.
Then I'll change it later, because it will then work.
Thank you very much!

Try starting the game with the controller off, and then once you get past the log in screen, turning it on.

The first tip was already Perfect.
I just tried it, even though I no longer had the controller activated in the options.
Switched it on in the game and everything works correctly straight away.
Thanks again!

Thank you!