I think you could do this in rule machine with your trigger being “changed.”
The key is to set a delay of 24 hours on your notification action, and to make the delay cancelable.
If the temperature doesn’t change, the delay elapses and the notification is sent.
But as long as the temp changes within 24 hours, a new instance of the rule will execute, and the prior instance (still in the delay period before sending notification) will be canceled.
Like this:
Personally, I do what @Alan_F does, which is to use an app designed to notify me when it receives no updates from a device after a defined period of time.
I like @bertabcd1234’s app Device Activity Check.