class ViewController {
    @IBOutlet weak var scrollView: UIScrollView!
    
    
    // ...
}

extension ViewController {

    func registerKeyboardNotifications() {
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(notif:)), name: UIResponder.keyboardWillShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(notif:)), name: UIResponder.keyboardWillHideNotification, object: nil)
    }

    @objc func keyboardWillShow(notif: Notification) {
        guard let frame = notif.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect else {
            return
        }
        scrollView.contentInset = UIEdgeInsets(top: 0.0,
                                               left: 0.0,
                                               bottom: frame.height - 100,
                                               right: 0.0)
    }

    @objc func keyboardWillHide(notif _: Notification) {
        scrollView.contentInset = UIEdgeInsets()
    }
}