CentOS8 made the decision NOT to include KDE however, it has been available via the EPEL repository.  Today they started upgrading the version on the EPEL respository but it is in a half updated broken state, so for now until they complete this project, KDE is not available on Centos8.

     I had bad feelings when Centos was taken over by Redhat, so far my instincts have proven to be right on, this was a very bad thing for the community.  All they’ve done is discontinue things and walk away from established standards, and support for non-paying non-Redhat customers is non-existent.