Have you run the ThumbTest.exe from https://nw-digital-radio.groups.io/g/ambe/files  ???

The ThumbDV™ appears to the operating system and applications as a simple serial device.  There is no user firmware to be loaded to the ThumbDV™  -- that warning is a 'red herring' that applies to other devices that BlueDV interacts with. 

The driver is simply the FTDI USB drivers (which on Windows should just automatically load and on Linux they are built in).  The serial (COM) port either is there or it isn't. 

If you can talk to the right COM port at the right data rate, using the test program for Windows (or the python scripts for Linux), then the ThumbDV™ is good --  it is then a configuration issue or an application/operating system issue to be debugged.