GTK4 (if Geany ever gets there) has a [native](https://docs.gtk.org/gtk4/class.FileChooserNative.html) file chooser for Windows and Macos, but not Qt (can't think why not ;-)
Actually, the native file chooser is indeed for Qt if the app calling it is run on Plasma or another Qt environment. The "native file chooser" just calls out to the XDG portal. And GTK3 already has that API as well.