How to make window fullscreen/maximized in Scene Builder?

You cannot do that using Scene Builder, since maximize or fullScreen are properties of the Stage and not the layouts set on the scene.

You can load and set the .fxml on the scene and later set the scene on the stage.

The following methods can be used on the stage :

• setMaximized(boolean) – To maximize the stage and fill the screen.
• setFullScreen(boolean) – To set stage as full-screen, undecorated window.