JavaFX runtime components are missing, and are required to run this application
To solve the issue, click on Run -> Run Configurations... -> Java Application, create a new launch configuration for your project and add these VM arguments:
Windows
--module-path "\path\to\javafx-sdk-15.0.1\lib" --add-modules javafx.controls,javafx.fxml
Linux/Mac
--module-path /path/to/javafx-sdk-15.0.1/lib --add-modules javafx.controls,javafx.fxml