As of V1.03 the NextionDriver has support for Nextion displays which are connected to the modem ('Port=modem' in MMDVM.ini) For this, it is necessary to use the MMDVMHost code dated 20180815 or later (G4KLX GitID #f0ea25d or later). It surely is OK when the MMDVMHost version string is 20180910 or later.
NOTE: When connecting a Nextion to the Nextion port on a MMDVM_HS hat, the Nextion screen default baud rate must be set to 9600 unless you build custom firmware and define a higher UART2 speed. Send the following serial command in the Nextion simulator "bauds=9600"
In the MMDVM.ini file, you must enable 'Transparent Data' and it's option 'SendFrameType', i.e. :
[Transparent Data]
Enable=1
RemoteAddress=127.0.0.1
RemotePort=40094
LocalPort=40095
SendFrameType=1
Then you can instruct NextionDriver to use the Transparent Data to connect to the display. This is done by setting the 'Port' option in the NextionDriver section of MMDVM.ini to 'modem'
[NextionDriver]
Port=modem
...
Data from the Nextion (when pressing buttons) will be treated similar and will exit MMDVMHost as transparent data. IMPORTANT : the firmware of the modem has to pass data from the display to MMDVMHost for this to work!
If this is not (yet) the case, you could ask the developer of your modem to add this feature.