I have never had anything other than a terrible experience with a Java app, under Windows, Linux (in GNOME 2 and Unity most of a decade ago, i3, or Sway). They always disregard platform conventions in both look and feel to a painful extent. But I will declare that I haven’t ever used IntelliJ, and I have no idea what it uses for its UI. But out of the box, Qt seems vastly better at matching platform look and feel, and generally gives you decent control over matching or not to match your requirements.
It looks mostly ok, but on Linux it doesn’t support smooth scrolling (even though this is supported by gtk). You also can’t use the meta key (windows key / cmd) as a modifier key for keyboard shortcuts. So I can’t configure intellij to use all the keyboard bindings I’m used to from macos. Again, this isn’t a problem with other gtk apps. It’s just (apparently) a platform limitation of whatever Java toolkit they’re using.
So in my experience it’s 95% of the way there. I certainly prefer it over Xcode, but it has issues that native apps don’t have.
First of all, up-to-date official packages are now published to Maven Central as part of the release process, so you can just add it as a dependency as easily as with any other library. Until recently you would have had to either fiddle around with Eclipse's alternative package management system, download it manually or use someone's unofficial Maven artifact. But that's now resolved.
Secondly, if you bundle a Java runtime customized with jlink (as is recommended these days), an SWT application is actually smaller than a Swing application. When you don't use Swing, you can exclude the entire "java.desktop" module, which is slightly larger than the SWT libraries.
