try turning off link angle in the linked camera behaviour
i made the camera work with the mouse like this and it works fine
this is my game so far : https://liluo.io/instant-builds/23f55b0d-0259-45a3-9ff5-984af52236f2
you can't actually do anything yet but the camera works
as you can see the sky is pink as i am trying to add a skybox
the variable sensitivity is just the sensitivity, try setting it to 10