Setting the environment variable SAL_USE_VCLPLUGIN=gen also disables the GTK menu and fixed the issue for me without uninstalling libreoffice-gtk.
Using LibreOffice 6.2.6.2 on Ubuntu 16.04.
The menu is ugly now, but not duplicated.
Setting the environment variable SAL_USE_ VCLPLUGIN= gen also disables the GTK menu and fixed the issue for me without uninstalling libreoffice-gtk.
Using LibreOffice 6.2.6.2 on Ubuntu 16.04.
The menu is ugly now, but not duplicated.