Greetings.
You have two options here.
If you bind the Mobilinkd TNC to your Pi using their Bluetooth drivers, you can use the Serial_TNC port type. However, if you have Bluetooth connectivity dropouts, this may hang or crash YAAC.
Another option is to use the Bluetooth plugin for YAAC and thereby let YAAC manage the Bluetooth connection (and deal with flakiness thereof) with the Bluetooth_TNC port type. It has a limited set of native libraries, so I'm not sure if the included armv5 library will work on a Pi4, but you can try it. No guarantees; I don't own that particular hardware, so I can't test it.
Hope this helps.
Andrew, KA2DDO
author of YAAC
