http://mmdvm.bi7jta.org/search/label/Nextion_Multi_DISPLAY

Firmware (.HMI)
PD0DIB  https://github.com/PD0DIB/Nextion_HAM-radio-screens
BI7JTA https://www.bi7jta.org/files/MMDVM_Nextion
F4EWI https://twitter.com/F4EWI_Thierry/status/1076438473387708416

Driver
https://github.com/PD0DIB/Nextion_HAM-radio-screens/wiki/FAQ-Nextion.driver-by-ON7LDS

Connect multiple Nextion displays @on7lds
https://on7lds.net/42/connect-multiple-nextion-displays?fbclid=IwAR15V-c1FHBvgcTwOIBVbBfBOHFOm0bXU3cUi8umRYTotIK_0G0hLtECD6E