Software updater in 18.04 prompted users that software updates (packages) were available. Since 18.10, unless you go looking for updates(Discover, Muon, sudo apt update) there is no indication that they are available.
Well, this sucks. Previous to Discover, Kubuntu was using update-notifier-kde with Muon, but that hasn't been updated in a long, long time. Now they don't use any of the update-notifier codebase and all the notifications are hidden within the stupid plasmoid widget.
So I guess we need update-notifier-gtk or we need to bring update-notifier-kde back.