| rest splunk_server=local /services/apps/local | search update.version=* | table title version update.version

If that Splunk has internet access, it’ll have the update.* fields filled with the latest version if there is an update available for any app installed on that system. The splunk_server filter should be usable for querying search peers as well. Using that scheduled daily or weekly, you could alert yourself of any update.

Got it here: https://answers.splunk.com/answers/336868/has-anyone-created-a-scheduled-search-that-notifie.html