For an existing JavaFX project (JDK 10), I have the option to switch to design (for class with the main method).
But if I do, it will be displayed.
It is quite logical. This is an editor for JFrame (Swing). For such JavaFX editing, you need to install the JavaFX Scene Builder.
So why is that option here? And why, at the new JavaFX project, the design tab is not.