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Worked for me in 2021. Started out with Tutorial - JavaFX for Beginners before merging that with this tutorial.
Don't forget to set your fx:id's...
Hey for anyone watching this thread later, I got JavaFX into IntelliJ in 2021 from this link: Configure JavaFX Scene Builder - Help | IntelliJ IDEA
Works very well for me in 2021! Thanks a lot man.