Someone asked me if turning a site into the communication site look and feel would give you the top navigation. The answer is no.
To get the top nav on any modern site – and by association, get the mega menu options – go to the SharePoint Admin Centre and register the site as a hub. It will then add the top navigation options for you. Or connect it to an existing hub, but then you lose the ability to have your own theme.
[…] If you want the top navigation to display too, turn it into a hub site. […]