I'm getting this error: WARNING: Unsupported JavaFX configuration: classes were loaded from 'unnamed module @c6018c6'. What should I do?

Question

Before I updated BlueJ this program worked fine, but now that I have updated to version 5.1.0 the program doesn't work and shows the above error message. If you need more info on the error message I can send the full list.

import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.Group;
import javafx.scene.shape.Line;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.input.MouseEvent;
import javafx.stage.Stage;

public class Source extends Application{
    public static Group MainGroup = new Group();
    public static Scene MainScene = new Scene(MainGroup);
    @Override public void start(Stage stage){
        stage.setScene(MainScene);
        stage.setFullScreen(true);
        
        stage.show();
    }
}```

Here is the full warning:

Jun 14, 2023 12:01:05 PM com.sun.javafx.application.PlatformImpl startup
WARNING: Unsupported JavaFX configuration: classes were loaded from 'unnamed module @c6018c6'
Exception in Application constructor
Exception in thread "JavaFX BlueJ Helper" java.lang.RuntimeException: Unable to construct Application instance: class Source
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:891)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:196)
    at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.NoClassDefFoundError: Could not initialize class Source