The issue that JavaFX is no longer part of JDK 11. The following solution works using IntelliJ (haven't tried it with NetBeans):
Add JavaFX Global Library as a dependency:
Settings -> Project Structure -> Module. In module go to the Dependencies tab, and click the add "+" sign -> Library -> Java-> choose JavaFX from the list and click Add Selected, then Apply settings.
Right click source file (src) in your JavaFX project, and create a new module-info.java file. Inside the file write the following code :
module YourProjectName { requires javafx.fxml; requires javafx.controls; requires javafx.graphics; opens sample; }
These 2 steps will solve all your issues with JavaFX, I assure you.
Reference : There's a You Tube tutorial made by The Learn Programming channel, will explain all the details above in just 5 minutes. I also recommend watching it to solve your problem: https://www.youtube.com/watch?v=WtOgoomDewo
