RM can't access that info. It is not a device attribute and as such changes to this timestamp doesn't generate an event you can capture in RM.
The likely explanation is that the device driver is filtering those updates instead of forwarding them to the hub.
Do you mean last update time or last activity at? They are different. In this image, I believe the "last update time" refers to the last time device preferences were saved (from the device details page).
You would need to be more than a Hubitat god, you would need to be a Zigbee/Z-Wave/Matter firmware god. For example, battery devices notoriously fail to respond to refresh requests (they are sleepy to save battery)
Really? Interesting. I didn't know that.
Suggestions by @User7221 apply to the last activity timestamp. You could also have a look at Simple Idle Alerts.
