Here are some relevant guidance:
And since you tagged iOS:
Make sure you 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 ).
Does it still not work? What ISP, what brand and model on the modem? Do you have any other boxes hooked up between Nest Wifi and the internet, like a switch or a router?