Thank you for the report.
To try it, I have just installed it & started it under LXDE:
 $ menulibre

(menulibre:3102): Gtk-WARNING **: 19:57:00.624: Theme parsing error: gtk.css:2:33: Failed to import: Error opening file /home/lewis/.config/gtk-3.0/window_decorations.css: No such file or directory
No menu prefix found, MenuLibre will not function properly.
(menulibre:3102): Gtk-WARNING **: 19:57:02.459: gtk_menu_attach_to_widget(): menu already attached to GtkMenuButton
(menulibre:3102): Gtk-WARNING **: 19:57:02.697: gtk_menu_attach_to_widget(): menu already attached to GtkMenuButton
WARNING:menulibre: getDefaultMenuPrefix() 'No menu prefix found, MenuLibre will not function properly.'
WARNING:menulibre: getDefaultMenuPrefix() 'No menu prefix found, MenuLibre will not function properly.'
WARNING:menulibre: getDefaultMenuPrefix() 'No menu prefix found, MenuLibre will not function properly.'
 but is started OK - one of those bare Gnome applications.
 I will go off to try it under Gnome.

CC: (none) => lewyssmith

Here under Gnome, real x64 hardware.

Starting 'menulibre' from terminal gave exactly the same output as comment 0 (except for a different initial number). Note, however, that the process *did not end*, but remained static after the last O/P:
    if not self.tree.load_sync():
gi.repository.GLib.Error: g-io-error-quark: Failed to look up menu_file for "gnome-applications.menu"
 (0)

It did not appear in any shape or form.
$ ps ax | grep menu
   4198 ?        Sl     0:01 /usr/bin/python3 /usr/bin/menulibre
   4613 pts/0    Sl+    0:01 /usr/bin/python3 /usr/bin/menulibre

After killing it Ctrl/C in the terminal, this still showed:
$ ps ax | grep menu
   4198 ?        Sl     0:01 /usr/bin/python3 /usr/bin/menulibre

This is something one can assign to wally, its maintainer.

CC: lewyssmith => (none)
Assignee: bugsquad => jani.valimaa

This is a bit problematic as GNOME doesn't use traditional app menus anymore. 

However I have updated menulibre to the latest release and added a patch to allow starting menulibre in modern GNOME env.

Please test menulibre-2.2.3-1.mga8 from core/updates_testing.

CC: (none) => jani.valimaa
Assignee: jani.valimaa => qa-bugs

menulibre-2.2.3-1.mga8 starts in a virtualbox VM Mag8 x86_64 Gnome session. From the menu and also from terminal.Only some warning in console left:

(menulibre:3998): Gtk-WARNING **: 11:38:44.939: gtk_menu_attach_to_widget(): menu already attached to GtkMenuButton

mga8, x86_64
Newly installed GNOME booted as GNOME on Xorg.
Before updating it behaved as Lewis indicated, crashing.
Installed the update but could not find it in the applications list so ran it directly from the command line and a gui appeared but there was nothing to indicate that it was menulibre.  It has a menubar with symbols for add, save, undo, redo, etc and search.
Then a message line "Invalid desktop files detected...." and a side menu for different software categories.  If Graphics is chosen the view panel has a tab at the bottom saying /usr/share/desktop-directories/mandriva-graphics.directory.

If that is what is expected then this looks OK.

CC: (none) => tarazed25

Launched in Mate menulibre showed up as under GNOME but with a frame labelled Menulibre.  So this does look OK for GNOME.

Whiteboard: (none) => MGA8-64-OK

Apologies - menulibre does turn up in the applications list as "Menu editor".

Validating.

CC: (none) => andrewsfarm

An update for this issue has been pushed to the Mageia Updates repository.

https://advisories.mageia.org/MGAA-2021-0234.html

Resolution: (none) => FIXED
Status: NEW => RESOLVED