One of the best new features of the modern SharePoint infrastructure is the introduction of hub sites. The only slight complication is that Hub Sites are created in their own site collection, which although this is great from a data protection security perspective, makes inter-site navigation a pain to construct and maintain.
So, to help us find a way round this Microsoft has introduced the Hub Site Navigation. Once a site has been designated as the Main Hub Site then you can add other sites under it and they can all share a single new navigation bar, and theme, which sits above the existing title section and below the office 365 bar.
Beware however when you add this - in some circumstances it does not work! I could not work out why this didn't work - although the menu appeared, the main existing menu was also there at the same time and there was no way to edit or manage either.
After many support calls to Microsoft, who to be honest, although they did get to us very quickly, but were useless, I managed to resolve the issue by trial and error.
I found that if you have the old classic SharePoint Publishing Infrastructure turned on and a site is using SharePoint server Publishing feature then this causes the new Manu system to fail.
So to resolve.....
- ensure in the site feature of each site in the collection that SharePoint server Publishing is Deactivated
Then go to the site collection features and ensure that the SharePoint Server Publishing Infrastructure is Deactivated
Once these two are off and once your cache has cleared you should fine all the menus can be edited correctly.
The Hub menu can be edited from the Hub Site (top level main site) using the edit link on the right end of the bar. This opens a vertical editor pane to the left of your screen. It does not automatically add menu items so it has to be done manually - but only once as it replicates through all sites links to the collection.
the other old menus can be edited in the navigation section of the site settings all all items removed.