KVO not working for `UIView.bounds` keypath when view resizing happens due to `autoresizingmask`

I have following view controller:

class ViewController: UIViewController {

  lazy var superView: UIView = {
    let view = UIView(frame: CGRect(x: 0, y: 0, width: 300, height: 300))
    view.backgroundColor = UIColor.white
    return view
  }()

  lazy var childView: UIView = {
    let view = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
    view.backgroundColor = UIColor.black
    return view
  }()

  var boundObservation: NSKeyValueObservation?

  override func viewDidLoad() {
    super.viewDidLoad()
    self.view.backgroundColor = UIColor.orange

    self.view.addSubview(self.superView)
    self.superView.center = CGPoint(
      x: self.view.frame.width / 2.0,
      y: self.view.frame.height / 2.0
    )

    self.superView.addSubview(self.childView)
    self.childView.center = CGPoint(
      x: self.superView.frame.width / 2.0,
      y: self.superView.frame.height / 2.0
    )
    self.childView.autoresizingMask = .flexibleWidth

    let button = UIButton(type: .system)
    button.setTitle("Tap me!", for: .normal)
    button.addTarget(self, action: #selector(buttonTapped(_:)), for: .touchUpInside)
    self.view.addSubview(button)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
    button.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor, constant: -24).isActive = true

    self.boundObservation = self.childView.observe(
      \UIView.bounds,
      options: .new,
      changeHandler: { view, change in
        print(change.newValue ?? "nil")
    })
  }

  @objc func buttonTapped(_ sender: UIButton) {
    let view = self.superView
    let previousSize = view.bounds.size
    view.bounds.size = CGSize(width: previousSize.width + 50, height: previousSize.height + 20)
  }
}

My childView get's automatically resized due to autoresizing mask when superView is resized. But KVO observation is not getting called. Why is KVO not working in this case?

My issue was solved by observing \.layer.bounds instead of \UIView.bounds because I learned that the layer is the “source of truth” for a view’s layout, so I suspected the autoresizing mask was directly modifying the layer bounds without going through UIView.bounds