The simulator shows white screen. Here is all the code:

class ViewController: UIViewController {

    var titleLabel = UILabel()

    override func viewDidLoad() {
        super.viewDidLoad()
        configureTitleLabel()
        // Do any additional setup after loading the view.
    }

    func configureTitleLabel(){
        view.addSubview(titleLabel)
        titleLabel.text = "text"
        titleLabel.font = UIFont.boldSystemFont(ofSize: 36)
        titleLabel.textAlignment = .center
        titleLabel.numberOfLines = 0
        titleLabel.adjustsFontSizeToFitWidth = true

        setTitleLabelConstraints()
    }

    func setTitleLabelConstraints(){
        titleLabel.translatesAutoresizingMaskIntoConstraints
        titleLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor,constant: 20).isActive
        titleLabel.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor,constant: 20).isActive
        titleLabel.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor,constant: -20).isActive

    }
}

Think you added the view.addSubview(titleLabel) before you have amended it put it after you have made the changes.