How do you install KDE Plasma on CentOS 8?

There are no package groups for KDE Plasma in CentOS 8, as there are in Fedora. But you can install KDE. KDE packages are in a repo called EPEL Playground. Register the repo below at dnf and follow the tutorial:

$ sudo dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm

$ sudo dnf config-manager --set-enabled PowerTools

$ sudo dnf install plasma-workspace

Plasma-workspace will give you a complete Plasma experience with all applications and applets.

EPEL is supported by Fedora maintainers. These maintainers work for IBM, which owns RedHat. Therefore, EPEL is fully supported by RedHat, although unofficially.