I normally just click on update indicator on the Activity Icon and have Notifications set up from Announcements (Watching) Plex Media Server and other.
Some new versions are not marked for auto-update immediately, but are only made available for manual download.
Just for the possible case, that there are suddenly many users reporting that this version has a serious bug.
It’s like tipping your toe into the water, to test if it’s too cold.
It also depends on which “update channel” you have selected for your server.
“Public” will only remind about versions which are listed as “available for all users” in the release notes Plex Media Server - #438 by emilybersin
i.e. no “beta” versions.