GTK3 looks almost exactly native (down to window tinting), except that the current version of breeze-gtk seems to struggle a bit with client-side decoration (the minimize/maximize/close buttons that are integrated in the toolbar), making them for example too big. (It's a known regression and should be fixed in the next version, though.)

GTK4 and the whole lack of libadwaita theming thing does look out of place though. But I use many GTK3 apps on KDE and they look near perfect. The only thing I can think of is some color-changes when gaining/losing focus are sometimes missing in Electron apps whose menu bar is themed via GTK3, iirc.