That “new” navigation was actually introduced more than 1 year ago 
If Plex is showing none of your libraries on its main navigation, you might want to “reset customizations” on the Plex home screen. This will let you pick your preferred server and libraries. If it’s just single libraries… open the “more” view, click the ... icon next to the library name and select to pin that library.
Back in the main navigation you can also re-order the libraries according to your liking.
Personally I like this feature a lot. It allows me to streamline the navigation of each device for its target purpose (e.g. living room tv shows main movie/tv show libraries + home videos; iPhone pinned the main movie/tv shows library and my music library; desktop PC has the full list of libraries pinned for immediate accesss).
