The 90 days message referred to compulsory registration for life time updates.
If not registered in those 90 days there will be no free updates afterwards.
Your old device was a so called Nav2 unit, using HOME to communicate with your computer.
Your new one is a Nav3 device that requires different software, to be downloaded from TomTom's web site. It is called MyDrive. You mat have documentation that calls this MyTomTom. The functions of bothe are the same it is just the MyDrive uses a more "modern" interface (to attract the kiddies?).
The new software does not recognize your device as an external drive, it now shows as a network adapter.
After you install MyDrive and start it it will put an icon in the task bar. When you click on that a small pop up window comes up with a line called Add community content.
There you can add POIs (Favorites are now in Favorite.ov2, a POI category), voices, screen colour schemes, the startup splash screen, warning sounds and carsymbols.,