For my main menu, I have a second camera which shouldn’t be moving up and down due to mouse movement but is, and I just would like to know if I can make this camera in a fixed position / angle
Drag it in the root of the scene hierarchy (no parents), or make sure that the parent it has isn’t being moved about. Also make sure the tag isn’t set to MainCamera.
Cameras don’t automatically respond to input, so I’m guessing you either attached the camera it as a child of something that IS receiving input (maybe even your other camera), or you have a script attached that’s explicitly moving it in response to input.