I started a new JavaFX application with the JavaFX project template that IntelliJ gives you that will only display a GUI created with Scene Builder with some line charts, as far as I'm concerned, the code is right and simple, it's just a test project.

Also, I can't visualize the .class file in IntelliJ

The message is:

Error occurred during initialization of boot layer
java.lang.module.FindException: Error reading module: C:\Users\pv3\Desktop\PruebasFX_OracleFXProyectInicio\target\classes
Caused by: java.lang.module.InvalidModuleDescriptorException: GraficasVentPrueba1.class found in top-level directory (unnamed package not allowed in module)
    
Process finished with exit code 1

My code:

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.stage.Stage;
import java.io.IOException;


public class GraficasVentPrueba1 extends Application {

    @Override
    public void start(Stage stage) throws IOException{
        FXMLLoader launcherGraficas = new FXMLLoader(GraficasVentPrueba1.class.getResource("GraficasVentPrueba1.fxml"));
        Scene emergenteGraficas = new Scene(launcherGraficas.load());
        stage.setScene(emergenteGraficas);
        stage.show();
    }
    public static void main(String[] args) {
        launch(args);
    }
}

It supposed to just open the .fxml. Instead it shows that error message