Netgear Nighthawk wifi range extender no longer works with Comcast XB7 modem

Thank you. However, I have tried using the smart setup installation assistant numerous times, but the assistant gets to the point where you have to select either of the newly set up Range Extender's 2G or 5G wifi connections on the device I am using to access the assitant (my iphone 11) and I can't select either one, because there is no signal to the extender.

   At this point, when I do try to connect to either the 2G or 5G connections on the extender in my phone's settings, I get a message on my phone that it is:

     Unable to join the network (extender 2G name)

If your netowrk security is managed by Wi-fi address (also known as "MAC Address"), you may need to turn off Private Wi-Fi Address or modify your network settings.

     Additionally, when I get to one of the set up steps in the Nighthawk setup and the prompt comes up saying it is installing my settings, the circle whirls around and around and then suddenly, I get a prompt that safari can't reach the internet and I am kicked out of the assitant. 

     I did read not to name the 2G and 5G connections differently and am using the same name and password for each. As I said, it was working perfectly until I installed the updated firmwared and launced a new Xfinity XB7 modem. I have to think one of them is causing an issue.