Problem with Nextion and GIGA r1 wifi

You will not find much support on this forum for using Nextion.h library.
Either use the methods of Perry Bebbington presented here
https://forum.arduino.cc/t/using-nextion-displays-with-arduino/580289

or alternatively the Easy Nextion Library by Seithan
https://www.arduino.cc/reference/en/libraries/easy-nextion-library/
https://github.com/Seithan/EasyNextionLibrary/blob/master/src/EasyNextionLibrary.h

The Giga R1 has multiple hardware serial ports, and using Software Serial should not be used,