Hello.
I know the Nextion and I know PICs, but not Aurdino (yet).
I've never tried any Nextion libraries, I write my own code to work the way I want it to. I can't imagine the host repeatedly querying the Nextion would work well at all, it would clog the serial port up with queries and be unresponsive for more than a few objects on the Nextion.
The way I do it is to put a series printh statements under the touch release event for every button on the Nextion. I send a series of bytes that identify the page and the button that has been pressed. I use interrupts on the PIC to detect receipt of the data from the Nextion and process it to do what I want.
I imagine the same is possible on an Aurdino without too much pain.
HTH