Multiple JInternalFrame windows are slow to drag

On Mac, there is a big delay when I create multiple JInternalFrame windows in JFrame and drag them around.

https://i.sstatic.net/Av15A.gif

there is a big delay when I create multiple JInternalFrame windows in JFrame and drag them around

public static void main(String... args) {
    System.out.println("Hello World!");
    JFrame mainFrame = new JFrame("Hello");
    mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    mainFrame.setSize(1920, 1080);

    JDesktopPane desktopPane = new JDesktopPane();
    mainFrame.setContentPane(desktopPane);


    for (int i = 0; i< 10; i++) {
        JInternalFrame internalFrame = new JInternalFrame("Hello");
        internalFrame.setPreferredSize(new Dimension(1800, 1000));
        desktopPane.add(internalFrame);
        internalFrame.setVisible(true);
        internalFrame.pack();
        // internalFrame.setDebugGraphicsOptions(DebugGraphics.LOG_OPTION);
    }

    mainFrame.setVisible(true);
}

No problem if debug is turned on.

internalFrame.setDebugGraphicsOptions(DebugGraphics.LOG_OPTION);

I have tested both Java 15 and Java 8 and both have this problem.

Does anyone know why there is a serious delay when dragging the JInternalFrame window?

for (int i = 0; i< 10; i++) {
    JInternalFrame internalFrame = new JInternalFrame(String.valueOf(i));
    internalFrame.setPreferredSize(new Dimension(1800, 1000));
    desktopPane.add(internalFrame);
    internalFrame.setVisible(true);
    internalFrame.pack();
    internalFrame.setOpaque(true);
    // internalFrame.setDebugGraphicsOptions(DebugGraphics.LOG_OPTION);
}

Adding internalFrame.setOpaque(true); can ease this problem.