Ignore the camera warning.
I already clicked the warnings and it brought me to this code in Unity's XRPass script:
public Rect GetViewport(int viewIndex = 0)
{
return m_Views[viewIndex].viewport;
}
I don't even know what this is and it doesn't throw an error in Visual Studio.
It is a bug in new versions of Unity. When you click an object that has a renderer in play mode, an error shows up. The bug has been reported and will be fixed soon. You can check here until the bug is fixed: Bug