I've been using a little matrix app of my own making that sends notificatins to a specific matrix room when big jobs complete. Its nothing fancy (and conceptually not different than slack notifications), and sysadmins have been leveraging email for the same exact purpose...but i like me some matrix...plus, said same matrix room can be made to receive other/outside notifications too; win-win!
Just a few days. It’s done by running an external service that joins rooms and listens for commands. We’re using maubot [1] since it’s one of the more popular ones, but it has some rough edges [2] [3] [4]. Our setup for just the “rss” plugin is dockerized and documented here [5].