I have an existing application that I am progressively adding JavaFX to. I have a Stage that I make with a menu, and I call setUseSystemMenuBar(true). However, on Mac this has no effect. I wonder if this could be fixed if possible, or if is intended behaviour that it does not work, if that could be documented somewhere. Steps to reproduce:

// A class that creates a scene with a menu and sets useSystemMenuBar to true:
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.VBox;

public class MenuScene extends Scene
{
    public MenuScene()
    {
        super(new VBox());
        MenuBar m = new MenuBar();
        Menu menu = new Menu("My Menu");
        menu.getItems().add(new MenuItem("My item"));
        m.getMenus().add(menu);
        m.setUseSystemMenuBar(true);
        
        ((VBox)getRoot()).getChildren().addAll(m, new Label("Content"));
    }
}

// It works if I call it from a JavaFX Application:
import javafx.application.Application;
import javafx.stage.Stage;

public class TestPureMenu extends Application
{
    @Override
    public void start(Stage stage) throws Exception
    {
        stage.setScene(new MenuScene());
        stage.show();
    }
}

// But not if I call it from an existing non-JavaFX application:
import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.stage.Stage;

public class TestEmbedMenu
{
    public static void main(String[] args) {
        // Initialise JavaFX:
        new JFXPanel();
        
        // Now make Stage:
        Platform.runLater(() -> {
            Stage s = new Stage();
            s.setScene(new MenuScene());
            s.show();
        });
    }
}