Are you certain the orange (blue) light in the left wing started flashing faster between Step 27 and Step 30?
The light is on the drone receiver, sometimes called the RF Module. It is actually a two way transceiver. If the light got faster, it means it is in communication with the mainboard of the drone. But if the ID is not showing up on the controller, it means it is NOT in communication with the controller. The possibilities are bad antenna connections in either the drone or the controller, or damaged RF modules in either the drone or the controller. The drone module would be suspect because of operating at low voltage, but the presence of the light indicates it is at least partially functional. Another possibility is the NFZ firmware has caused an issue.
Have you recently opened either the drone or the controller?
Do you have another controller, or another drone available for testing?
Did you make any changes to the controller firmware?
Also, are you sure you are using a "Data Capable" USB cord when connecting the drone to the GUI? An ordinary charging USB looks exactly like a "Data" USB, but will not work for file transfer or GUI. I assume you had a data USB when you installed the NFZ firmware. Are you sure you are using the same USB cable?
One last thought. You mentioned your Q500 is a Q500 4K. If that is correct, the GUI plug in the battery door is a one sided plug. If you have a different Q500 model, there are two sets of wires plugged together. Either way, that plug is often hit by the battery during installation and removal. The pins get pulled out, and that may be another thing to check to figure out why the GUI is not working. If you can get the GUI to work, you may be able to uninstall that NFZ firmware. And on an older model with two sets of wires plugged together, that is the path between the receiver and the mainboard.