Have wired as follows
Nextion TX to Arduino (Nex) RX
Nextion RX to Arduino (Nex) TX
Arduino (Nex) RX to SerialMonitorArduino TX
Common GND to all boards
Have wired as follows
Nextion TX to Arduino (Nex) RX
Nextion RX to Arduino (Nex) TX
Arduino (Nex) RX to SerialMonitorArduino TX
Common GND to all boards