Is your hub 3 set to provide a WiFi signal Sonos can hear?

https://support.sonos.com/en-us/article/supported-wifi-modes-and-security-standards-for-sonos-products

Wi-Fi isn’t seen by Sonos one when searching on App

reset and factory reset completed on hub3 still cannot see the Sonos. Plugged in Smart Hub 2 and Sonos is visible and connected straight away

Did you add the new routers SSID/credentials to your speaker? If not, then see this Sonos Support link:

https://support.sonos.com/en-us/article/connect-sonos-to-a-new-router-or-wi-fi-network