Have you read and followed these setup instructions?
You might find addition things to try in earlier threads, like this one:
And since iOS is mentioned.
Make sure the device used for the setup process with the Google Home app have no VPN enabled/ connected; not any 3rd party product, nor the "Apple iCloud Private Relay" ( https://support.apple.com/en-us/HT212614 ).
Make sure the Google Home app has been granted permission for "local network access" ( https://support.google.com/chromecast/answer/7172427?hl=en ).
Make sure that proxy is set to disabled while connected to the Nest Wifi network ( https://www.expressvpn.com/support/troubleshooting/disable-proxy-safari/#ios ).
IPv6 on Nest Wifi has caused strange problems lately. One thing to try is to disable IPv6 ( https://support.google.com/googlenest/answer/6361450?hl=en ), add new Nest Wifi unit, then leave IPv6 off or enable it again.