> stage.getIcons().add()
Doesn't work and never did on MacOS.
EDIT: bug (closed as won't fix!!): https://bugs.openjdk.java.net/browse/JDK-8095033
> opening some URL in the system browser
HostServices also does not work in all but Oracle's distribution of JDK 8, which is abandoned now: https://github.com/javafxports/openjdk-jfx/issues/540
> Doesn't work and never did on MacOS.
Gotcha, I work only with Linux and Windows. There was a problem where the icon was incredibly pixelated on Windows 7, but they fixed that.
> HostServices also does not work in all but Oracle's distribution of JDK 8
I see, I tested it only on Bellsoft's JDK 11, since I don't use 8 anymore.
As in stage.getIcons().add()? Or do you mean for the binary that jpackager produces? I wrap my apps with launch4j which allows that. Then I bundle them with jlink-made JRE (about 60 MB). Works pretty well, total size is ~100MB for the whole app with all the dependencies, (not a Hello World app by any means).
>opening some URL in the system browser
As in getHostServices().showDocument("https://google.com")? Then again, nothing's stopping you from using awt's Desktop class, not sure I understand the problem here.