Top level menu doesn't work if sub page is present in Voyager theme

Most of the themes I have used allow you ‘main’ pages, and then sub levels.
So for example I may have a software product page, and nested within that , a buy now page , a demo page and so on.

Normally, I click on the Main link and it opens the main page.
Or I select the sub menu and I get the sub page.

In Voyager theme, the top level menu item does not ‘goto’ the page.
I can only select Top level menu items that have no children, or (if they do), the child pages.

Why is that… how can I fix it?

This is by design. The top-level item, called the parent, is turned into a placeholder for the child pages when they’re present. This is how the theme is designed to work.

Sadly that makes it incompatible with other themes and makes swapping from one theme to Voyager impossible. No use to me then.