Plus Java Swing was conceptually replaced by JavaFX, and there's an unwritten expectation that JavaFX should be used, as Swing is not really developed anymore.

Plus Java Swing was conceptually replaced by JavaFX, and there's an unwritten expectation that JavaFX should be used, as Swing is not really developed anymore. The only practical solution that I've found when it comes to writing portable desktop GUI applications was C++/Python and Qt. The "C++/Python" part is because the Qt bindings really exist for these two languages. It's possible to use a different language as well, but as you've said, that's an uphill battle as well. Nowadays there are also some new frameworks like Flutter Desktop, or Compose Multiplatform, but I haven't used them (just used Flutter on mobiles, and the development part was fun, the deloyment part not so fun). I never could overcome my dislike for Gtk+ development, especially for new versions. Gtk+ for me ended with version 2.0 :)