Presumably you’re referring to VARA FM? VARA is a proprietary, closed-source, Windows-only software modem, so I’m not sure what behavior you’re expecting in this case.
The mobilink will do the vara fm if I remember right but I can’t get the 74 with the bb link and it to connect to a packet node that is a vara node with it.
Mobilinkd is an AX.25 packet TNC, much like the internal packet TNC of the TH-D74. VARA FM is a completely different protocol. It is proprietary, and the only implementation is the closed source VARA FM software, which runs on Windows.
If you want to connect to a station using VARA FM, you need the VARA FM software. That means using a Windows computer, or a device capable of running or emulating Windows. The computer must also be connected to your radio through a sound card interface such as the Digirig Lite.
I put together a series of videos that walks through setting up a portable VARA FM station: