JLabel cannot be aligned Vertically

I am aware that they are answers to this questions but It doesnt work for me at all.
I tried :

   /*
     titleTextLabel.setAlignmentX(JLabel.CENTER_ALIGNMENT);

     titleTextLabel.setAlignmentY(JLabel.CENTER_ALIGNMENT);

     titleTextLabel.setHorizontalAlignment(SwingConstants.CENTER);
     titleTextLabel.setVerticalAlignment(SwingConstants.CENTER); also JLabel.CENTER 
 /*

But it didnt worked at all.
Here it is full code if someone wants to check .

If You think problem is on JFrame side it is not.There isnt a place to make failure (basic normal stuff)

Also I am adding photo of this code and also of application :https://i.stack.imgur.com/LKhku.jpg

    package com.practice;
    
    import javax.swing.*;
    import java.awt.*;
    
    public class Start extends JFrame {
    //Tutaj ustawiamy frame i pierwsze panele z napisem start
    
    
        // J-Obiekty itd
    
       private JPanel titleTextPanel, titleButtonPanel;
       private JLabel titleTextLabel;
       private JButton titleButton;
    
        Start(){
    
            this.setSize(1000,800);
            this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            this.setLayout(null);
            this.setLocationRelativeTo(null);
            this.getContentPane().setBackground(Color.darkGray);
    
    
            setUpStart();
    
            this.setVisible(true);
        }
    
      private   void setUpStart(){
            titleTextPanel=new JPanel();
            titleTextPanel.setBounds(200,50,600,150);
    
    
            titleTextLabel=new JLabel();
            titleTextLabel.setFont(new Font("Arial",Font.PLAIN, 30));
            titleTextLabel.setAlignmentX(JLabel.CENTER_ALIGNMENT);
            titleTextLabel.setAlignmentY(JLabel.CENTER_ALIGNMENT);
            titleTextLabel.setText("ASCENDING DARKNESS");
            titleTextPanel.add(titleTextLabel);
            this.add(titleTextPanel);
        }
    }

You have a couple issues, first why do you have the second JPanel? The JLabel is not getting centered in the JPanel because it has a flow layout.

Instead of using the second JPanel you can just use the JLabel.

  private   void setUpStart(){
        titleTextLabel=new JLabel();
        titleTextLabel.setBounds(200,50,600,150);
        titleTextLabel.setFont(new Font("Arial",Font.PLAIN, 30));
        titleTextLabel.setHorizontalAlignment(JLabel.CENTER);
        titleTextLabel.setVerticalAlignment(JLabel.CENTER);
        titleTextLabel.setText("ASCENDING DARKNESS");
        titleTextLabel.setOpaque(true);
        titleTextLabel.setBackground(Color.WHITE);
        this.add(titleTextLabel);
    }