When there is an update for Plex Media Server, the update notice you receive on the server dashboard is displaying a different version number than what has been released. Look at the version number on the file downloaded compared to the version the page says is available. The version numbers don’t match and haven’t done so in over a year. Happens on both beta and normal channels. This isn’t just a little minor the number is barely off either. It’s off by a whole revision.
While there isn’t an updater there is a notice that pops up when an update is available. And a page that provides some details (including links to release notes and to the download page). I believe that’s what the OP is referring to.