Error reporting and resolution of #selector above swift5

The version of swift has changed a lot recently. If you add an event to a button, you must be very skilled in OC. How do you define functions and pass parameters in
swift

 let btn = UIButton()
 btn.tag = 2
 btn.addTarget(self, action: #selector(buttonClick(button:)), for: .touchUpInside)

  @objc func buttonClick(button: UIButton) {
       button.isSelected = true
       print(btn.tag!)
        print("\(btn.tag)")
 }

The custom method must be preceded by @ objc to follow the OC mechanism, otherwise an error will be reported