Did I miss something obvious, I just had to replace a Nest 3 with a Nest 4. Added it to the google home app, same that it had matter support so deciced to add it to Hubitat, simple right ?
Went to Add device, Matter and was given the instructions to use the Google Home App to generate the 11 digit code. Followed the instructions given, despite the fact that Google Home App could control the thermostat without a problem it reported device not connected every time I asked to genreate the code. So, back + forth with Google, eventually told to use the thermastat to generate a QR Code.
But what next ? I couldn't see anyway to consume the QR code from the Hubitat App (There is an option for Z-Wave, should I have used that ?). Eventually I had Claude decode the QR Code and give me the 11 digit code which worked, although the device then appeared as a generic matter hub, and I to manually switch it to Google Matter Nest Thermostat.
Not actually sure that driver is actually working, that's today's project. 
