UIMenubuilder not called (Catalyst)

I have an iOS app (create feb 2019) which is now also available for MacOS by using Mac Catalyst.

The app works fine. I added menu functionality to the File menu with

override func validate(_ command: UICommand) {

}

Now I want to remove the Help menu.

For this I used, buildmenu in AppDelegate.

override func buildMenu(with builder: UIMenuBuilder) {
  super.buildMenu(with: builder)
  builder.remove(menu: .help)
}

In a newer app (Dec 2019) for Catalyst this works fine, and the code removes the menu.

In my older app, buildMenu is not called.

AppDelegate is setup as a UIResponder...

I have no idea how to make this work.

Any idea what I can try?

Best regards.