@Mfarban The scene needs some camera to initialize. Keep the existing camera tagged MainCamera in the scene and destroy it right at the startup. After that replace it with the new one. So I would do this
void Awake()
{
Camera cam = Camera.main;
GameObject newCam = new GameObject("newMainCam");
newCam.AddComponent<Camera>();
if(cam) Destroy(cam.gameObject);
}