How do I hide a UIBarButtonItem?

Yes, I understood that was your question.

So, please show the code where you create the button.

What I did, with a right button:

In viewDidLoad:

        let rightButton = UIBarButtonItem(title: "Sa Riera", style: .plain, target: self, action: #selector(logoutUser(_ :))) // A nice name…
        self.navigationItem.rightBarButtonItem  = rightButton

Declare the Action func

    @objc func logoutUser(_ sender: UIButton) {
        print("Right Button")
    }

Then, I create a button to toggle the isHidden of the bar button, removing or recreating the button:

    @IBAction func showHideRightBarButton(_ sender: UIButton) {
        if self.navigationItem.rightBarButtonItem == nil {
            let rightButton = UIBarButtonItem(title: "Sa Riera", style: .plain, target: self, action: #selector(logoutUser(_ :)))
            self.navigationItem.rightBarButtonItem  = rightButton
        } else {
            self.navigationItem.setRightBarButton(nil, animated: true)
        }
    }