@Dfusconi
If you have a 1st gen Google Nest Outdoor Camera installed in the Google Nest app, you might be able to go to Settings in the Google Nest app, select "Home info", then "Home Wi-Fi help", and then select your camera and update the Wi-Fi settings. (I think you may have to do that while still on the original Wi-Fi network.). If that does not work, then you need to remove your camera from the Google Nest app, which performs a factory reset (again, while still on the old Wi-Fi network). Then you should be able to reinstall.
By the way, to install, you either need to scan the QR code on the back of the camera, or enter the 6-character alphanumeric setup code on the back of the camera (near the QR code).
If you can't do either of these, you may need to wait up til 60 days for the video history on your camera to expire:
https://support.google.com/googlenest/answer/9249728
OR, you can set the network name (SSID) and password on your new Xfinity router/modem to the same values used on your old router/modem. This is Google Nest's first recommendation. That's what we did when we got a new Xfinity router/modem a couple of years ago.
https://support.google.com/googlenest/answer/9223711
