I tried playing my game I’m currently developing and the first person controller is inverted. I did not touch the main camera and it turned out like this suddenly, it wasn’t like this before and the FPS Controller is fine in other projects.
Did you happen to add it twice? Have you tried disabling every other script in the game? Try deleting the standard assets folder and reimporting it.
If none of these work you may need to provide some more information on your setup.