How to draw objects from another class in JPanel?

Question

Java

I'm trying to make a small game and ran into a problem with drawing objects.
Main class.

public class Main {
  public static Frame frame = new Frame();
  public static JPanel[] panels = {new Game(), new Menu()};
      
  public static void main(String[] args) {
     frame = new Frame();		
     frame.add(panels[0]);		 
     frame.add(panels[1]);	
     
     if(panels[1].isVisible()) {
       frame.remove(panels[0]);
       panels[0].setVisible(false);
     }
     if(panels[0].isVisible()) {
       frame.remove(panels[1]);
       panels[1].setVisible(false);
       ((Game) panels[0]).start();
     }		 
  }
}

The constructor of the Frame class contains a timer that updates its contents.
Launches the menu bar first

public class Menu extends JPanel {		
  public Menu() {		
    JButton btn = new JButton("Start");
    add(btn);
    btn.addActionListener(new ActionListener() {			
      @Override
      public void actionPerformed(ActionEvent arg0) {
        Main.frame.add(Main.panels[0]);
        Main.frame.remove(Main.panels[1]);				
        Main.panels[0].setVisible(true);
      }
    });		
  }	 		 
  public void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D)g;
    g.setColor(Color.BLUE);
    g.fillRect(0, 0, Frame.frameW, Frame.frameH);		
  }
}

When you click on the button, Frame switches to the game panel

public class Game extends JPanel implements Runnable {	
  public static int WIDTH = Frame.frameW, HEIGHT = Frame.frameH;			
  public Thread thread;	
  private BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);;
  private Graphics2D g = (Graphics2D) image.getGraphics();	
  public static GameBack background;
  public static Player player;
  
  public Game() {		
    super();
    setPreferredSize(new Dimension(WIDTH, HEIGHT));
    setFocusable(true);
    requestFocus();						
  }	
  public  void start() {
    thread = new Thread(this);
    thread.start();
  }	
  public void run() {						
      background = new GameBack();
      player = new Player();		
    while(true) {										
        gameUpdate();
        gameRender();
        gameDraw();						
      try {
        Thread.sleep(33);
      } catch (InterruptedException e1) {				
        e1.printStackTrace();
      }
      }
      
    }		
  public void gameUpdate() {		
    background.update();
    player.update();					
    }			
  public void gameRender() {		
    background.draw(g);
    player.draw(g);				
  }	
  public void gameDraw() {
    Graphics g2 = this.getGraphics();
    g2.drawImage(image, 0, 0, null);
    g2.dispose();
  }
}

The game panel should draw the background and the player, which are registered in separate classes, but for some reason this does not happen.
Background class. The player class is built on the same principle.

public class GameBack {
  private Color color;
    
  public GameBack() {		
    color = Color.BLUE;		
  }	
  public void update() {		
  }	
  public void draw(Graphics2D g) {
    g.setColor(color);
    g.fillRect(0, 0, Game.WIDTH, Game.HEIGHT);		
  }
}

Please help me understand why this is not working. Thanks in advance