Well, Swing is still bundled with Java. Netbeans uses the "Flat Look and Feel" and looks ok to me. I find Swing a lot more work compared to FX.
JavaFX used to be bundled with Java, but was removed. Some JDK distributions bundle FX like it was before, and adding FX to a new project is simple and straight forward. Maven packages it nicely, and it includes the platform specific binary parts. If you can use Log4j, you can use Java FX. Onboarding onto FX is not a high bar.
I can not speak to SWT.
There's several examples of "modern" UIs in FX, I can't speak to any of them, I don't pay much attention to that space. It's imperfect compared to the web, but not impossible.
JavaFX used to be bundled with Java, but was removed. Some JDK distributions bundle FX like it was before, and adding FX to a new project is simple and straight forward. Maven packages it nicely, and it includes the platform specific binary parts. If you can use Log4j, you can use Java FX. Onboarding onto FX is not a high bar.
I can not speak to SWT.
There's several examples of "modern" UIs in FX, I can't speak to any of them, I don't pay much attention to that space. It's imperfect compared to the web, but not impossible.