SUMMARY On a KDE installation with global menu, gparted displays its menu on both the global menu bar as well as on a menu bar at the top of the application's window. STEPS TO REPRODUCE 1. launch gparted on a KDE system with global menu set up. OBSERVED RESULT application menu is displayed in both the global menu bar and locally on the top of the application's window. EXPECTED RESULT application's menu is displayed on the global menu bar only. Linux/KDE Plasma: Manjaro KDE Plasma KDE Plasma Version: 6.3.6 KDE Frameworks Version: 6.16.0 Qt Version: 6.9.1 ADDITIONAL INFORMATION gparted 1.7.0 Other Gnome applications such as gnome-terminal correctly use the global menu bar only. This blog here claimed that (on Plasma 5) gparted had no global menu since it was run as root: https://blog.broulik.de/2018/03/gtk-global-menu/ Now with the current software it does at least have a global menu. As an additional (maybe helpful) information, parted does not use the global menu at all on XFCE with vala-panel-appmenu.
This is a Gparted bug; it's up to the app to hide its in-window menubar if its menu gets exported. There's nothing any KDE code can do to force the app to do this.
I now opened https://gitlab.gnome.org/GNOME/gparted/-/issues/289