I was able to link my Gen 4 Nest thermostat using the pairing code

I got the pairing code though Google's "Home" App

(Google Home App -> Thermostat -> Gear Icon -> Device Information -> Linked Matter Apps & Services -> Link Apps and Services -> Use pairing code)

then added it using the UD Mobile app
(Settings -> Matter -> Add Matter with Setup code)

After a minute or so, the device was added, unfortunately only as a 'On-Off Switch'
(the thermostat does respond to the On-Off commands)

According to sources temperature and fan control are available

<nodeDefs>
    <nodedef nls="103" id="ZM00002_001_1">
        <sts>
            <st editor="ZM_OFF_ON_UNKNOWN" id="ST"/>
            <st hide="T" editor="ZM_ERR" id="ERR"/>
        </sts>
        <cmds>
            <sends/>
            <accepts>
                <cmd id="DON">
                    <p optional="T" editor="ZM_0_100_PERCENT" init="ST" id=""/>
                </cmd>
                <cmd id="DOF"/>
                <cmd id="TOGGLE"/>
                <cmd id="QUERY"/>
            </accepts>
        </cmds>
    </nodedef>
</nodeDefs>

<nodeInfo>
    <node flag="128" nodeDefId="ZM00002_001_1">
        <address>ZM00002_001_1</address>
        <name>ZM 002.1 On-Off Switch</name>
        <family>15</family>
        <hint>48.32.50.53</hint>
        <type>255.1.255.255</type>
        <enabled>true</enabled>
        <deviceClass>0</deviceClass>
        <wattage>0</wattage>
        <dcPeriod>0</dcPeriod>
        <startDelay>0</startDelay>
        <endDelay>0</endDelay>
        <pnode>ZM00002_001_1</pnode>
        <rpnode>ZM00002_001_1</rpnode>
        <typeInfo>
            <t val="103" id="ioxType"/>
            <t val="0" id="mfgCode"/>
            <t val="" id="model"/>
        </typeInfo>
        <property name="" uom="78" formatted="On" value="100" id="ST"/>
    </node>
    <properties>
        <property name="" uom="78" formatted="On" value="100" id="ST"/>
    </properties>
</nodeInfo>

Edited November 4Nov 4 by evilpete
update On-Off functionality info

I just tried this, and it sort of works. Two devices were added: a ZM 002.1 On-Off Switch and a ZM 002.1 Thermostat. I don't have any sort of Google Hub, which I thought was required to link a Nest thermostat.

The "switch" turns the heat pump off or back to its previously set mode.

The thermostat seems to work, except for "fan only." Unfortunately, that's one option I need. "Fan only" returns an error code. I can change the temperature. Almost there.

Just got back in town after being gone for several months. Upgraded last night to IoX 6.0.3 and PG3x 3.4.6 before adding the Nest to Matter today.

Edit: There are several options that return an error code besides "fan only."

Edited Saturday at 07:04 PM2 days by auger66