Adding a Google Nest Mini for Voice Control

I am trying to follow the instructions here to add a Google Nest Mini in a room which has an old Play 1 for voice control.

I can’t for the life of me add it in the Sonos app. Basically I get to the stage where I go into my Sonos app, General Settings add voice assistant. One of the devices on my system is an Arc, which has the ability to install / have Google Assistant. So when I select Settings->General Settigns->Voice Assistants->Add a voice assistant->Google Assistant it comes up with a prompt ‘select a room to add Google Assistant’ and presents me with the room with the Arc in.

There is no option to add my Nest Mini. I must be missing something but for the life of my I’ve got no idea what I need to do.