Sounds like you've already tried some troubleshooting steps but I'll include them here in full:
If none of the steps above help, factory reset your Chromecast and then retry setup. You may also want to try setup using a different phone or tablet, just to test, if you have one.
I appreciate your help here, davidking.
alixuny, how's it going? Have you tried the steps shared by davidking? If yes, how was it?
If you're still having trouble, please also try to manually connect to the Chromecast SSID. Here's how: go to the phone settings > Open Wi-Fi and connect to the Chromecast SSID (Example: Chromecast1234, Living Room TV, Bedroom TV, etc.) > Go to the Google Home app and try to set it up again.