For those with Kubuntu as you may have known, they replaced kpackage manager with Muon package manager.
If you were like me and accidentally clicked on the Muon software center and wondered where all of the functionality went don't panic, it is all still there. While the software center kept the same icon as the package manager, there is a little brown icon hidden away which is the Muon package manager. That is the one you want for all of the old kpackage functionality.