In other words: outdated, ugly and barely supports modern requirements such as high dpi. Apart from Jetbrains who put in a literal buttload of engineering, there is not a single Java Swing application that is not an absolute PITA to use.

Swing generally looks like the native widgets set. And how is it outdated? It's not like GUI programming has changed much.

I‘m sorry but have you been living under a rock? SwiftUI, UWP and Jetpack Compose are platforms that differ extremely from the way Swing works. Swing on macOS looks like OS X 10.9 (still uses Lucida Grande as the System Font), we’re 5 releases past that. On Windows, it looks like Vista, we’re past that, too, see modern apps such as the Terminal.

I don't think the inversion of control that SwiftUI or Jetpack Compose do on MVC is particularly fundamental. Factoring out the diffing of state when an observer is notified of updates into a single place can be a useful thing to do in certain cases, such as when a bunch of teams are all putting things on the screen and you don't want one of them to screw up the update loop for everyone (thus Facebook's use of React), but it makes the creation of composable views less straightforward, and you end up with the new problem of annotations to try to keep recalculation of the whole UI from being a performance problem. In MVC, a compound view can usually short circuit updates of its child views very naturally when there are no changes needed.

I just opened a couple of Swing programs on macOS. Other than not having dark mode, I couldn't see any major difference. I can't check it on Windows right now.

So, no, I don't live under a rock.