I tried the exact code from the JET example (https://amers2.apps.cp.thomsonreuters.com/Apps/JET/1.12.4/Web/apidoc/JET.html#updateAppMenu), but it did nothing. And the only other example I could find is specifically in the .NET API documentation (https://developers.thomsonreuters.com/app-studio/app-studio-.net-sdk/learning?content=4103&type=learning_material_item)
How do we customize the app menu if we're using the App Studio - Web SDK?
There is an example in the JET.js API Demo application. You can select it from the Developer menu or use this URL: cpurl://apps.cp./apps/JET in Eikon.
The sample code is under Core Functionality -> Customize AppMenu section. After applying the code, the AppMenu will look like: