Google Assistant has not been supported as a voice assistant on new Sonos devices for over 18mths.

The support for only Sonos Voice Control and Alexa is detailed under the FAQ on the Arc Ultra’s product page.

Sonos CEO previously stated the following around Google changing the implementation for Google Assistant:

“Right now, it’s a pretty heavy engineering lift for us to implement what they’d like any third party to implement. The change isn’t just impacting us. All of the companies that support Google Assistant from a third-party perspective need to assess is the work worth the effort? Right now, we don’t see it being worth the effort. We hope Google will take another path that will allow us to continue to offer it in more of a lightweight manner the way we do today. But we also feel well covered with what we have with both Alexa and Sonos Voice Control.”

Essentially, Google changed the requirements for ‘new’ devices. 

But Sonos will still work with GA using a Nest Mini. Just set the Ultra as a preferred speaker.