I'm really confused now.
The fullscreen property actually isn't updated just when you interact with the toggle. The toggle simply sets a variable in the code and the program updates the fullscreen property to align with said variable. This means that whether you interact with the toggle or not, the program makes sure that they match up.
Regarding your second point, nothing in the code stops the rotating script from working. When you start the game, the program starts at the main menu. How Unity works (which is what I used to make the game) is that different parts of the game are placed into different scenes. In this case, I have a main menu scene and a game scene. Starting the game simply loads in the new scene.
The main menu is just a dummy level. It's not playable and is purely aesthetic. The camera rotation is also aesthetic. There's no way for the camera to rotate in the actual game as I am using an entirely different camera with a different script in a different scene.
I still don't understand the problem, so maybe if you could show a video or something, that would be a little more help in terms of figuring out what's actually going wrong with the program?