title: SceneKit scene higher than expected FPS on macOS
body: <p>My macOS app has two <code>SceneKit</code> <code>sceneViews</code>, and when they're empty, they both appear to be running at an FPS of 120. </p>
  
  <p>I've not manually set <code>preferredFramesPerSecond</code> anywhere in my code. The default for <code>preferredFramesPerSecond</code> is 60 FPS, so I'm a bit confused as to why the FPS is double than that - anyone have any thoughts?</p>