Main menu example does not add menu, just the command

Description

When I follow the instructions and run the main-menu example, no menu is added just the command in the command pallet. I believe this is because some automatic loading of the schema for the menu does not work. I tried to use the code in a new project using the latest stable jupyter (^4.0.0). It behaved the same.

Reproduce

Follow the instructions in the example project.

No menu is added to Jupyter.

Expected behavior

I expect a menu to be added as per the description and animation.

Context

Operating System and version: Linux Ubuntu 22.04
Browser and version: Firefox & Chrome as of June 2024
JupyterLab version: version pinned in repository and ^4.0.0

In a new clean project, I am able to build a menu using code such as this:

import {
  JupyterFrontEnd,
  JupyterFrontEndPlugin,
} from '@jupyterlab/application';

import { IMainMenu } from '@jupyterlab/mainmenu';
import { ICommandPalette } from '@jupyterlab/apputils';

import {
  MenuSvg
} from '@jupyterlab/ui-components';

/**
 * Initialization data for a main menu extension.
 */
const extension: JupyterFrontEndPlugin<void> = {
  id: 'main-menu',
  autoStart: true,
  requires: [IMainMenu, ICommandPalette],
  activate: (app: JupyterFrontEnd,
      MainMenu: IMainMenu,
      palette: ICommandPalette) => {
    const { commands } = app;

    // Add a command
    const command = 'Item-1:JPSLMenu2:main-menu';
    commands.addCommand(command, {
      label: 'Item 1',
      caption: 'Item 1',
      execute: (args: any) => {
        console.log(
          `Item 1 has been called ${args['origin']}.`
        );
        window.alert(
          `Item 1 has been called ${args['origin']}.`
        );
      },
    });

    // Add the command to the command palette
    const category = 'JPSL Tools';
    palette.addItem({
      command,
      category,
      args: { origin: 'from the palette' },
    });

    // Add a menu using API
    const menu = new MenuSvg({ commands });
    menu.title.label = "JPSL Tools";
    menu.addItem({
        command: command,
        args:{label: "Item 1", origin: "from the menu"}
        });
    MainMenu.addMenu(menu);

The main-meu example in this repository is trying to do something else that does not appear to work currently.

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jupyterlab / extension-examples