recognizes when a AVPlayerController changes to full screen or back. There you can handle auto rotation behavior or other smart things

UIView-With-AVPlayerController.swift

// add your view as observer
func addVideoBoundsObserver(){
  playerController?.contentOverlayView?.addObserver(self, forKeyPath: "bounds", options: .new, context: nil)
}
    
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
  if keyPath == "bounds" {
    guard let new = change?[NSKeyValueChangeKey.newKey] as? CGRect
      else { return }
    
    if new.size == UIScreen.main.bounds.size {
        print("Player in full screen")
    } else {
        print("Player not in full screen")
    }
  }
}

// dont forgett to remove the observer!
deinit {
  playerController?.contentOverlayView?.removeObserver(self, forKeyPath: "bounds")
}