For those of you who want to use KDE on RHEL9 Beta, or CentOS Stream 9, it is available via EPEL.  It is currently plasma 5.23.5, kf5 5.90.0, qt5 5.15.2.  There might be an update before RHEL 9.0 is released.

There is currently a critical selinux bug[1] that prevents KDE from starting.  That is the reason I have not sent this out earlier.  When that get's fixed, I'll update these instructions.

Note:  All these steps should be done as sudo or root.

Step 0 - Manually fix selinux bug
  setsebool -P selinuxuser_execmod 1

Step 1 - Enable CRB and Install epel-release [2]

# RHEL 9 Beta
  subscription-manager repos --enable codeready-builder-beta-for-rhel-9-$(arch)-rpms

  dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm

# CentOS Stream 9
  dnf config-manager --set-enabled crb
  dnf install epel-release epel-next-release

Step 2 - Install KDE

  dnf group install "KDE Plasma Workspaces"
or
  dnf group install kde-desktop

There is a bug in the epel9 comps file (my fault, fixing now), so "KDE Plasma Workspaces" will not work without an exclusion.
So, for the next week or so, use the following to install the KDE Plasma Desktop from epel9
  dnf --exclude=rhc group install "KDE Plasma Workspaces"
or
  dnf group install kde-desktop

Step 2.a - (Optional) Install other kde groups

  dnf group install kde-media
  dnf group install kde-apps
  dnf install okular

Step 2.b - (Optional) Set sddm as desktop manager

  dnf install sddm\* -y
  systemctl enable sddm -f

Step 3 - Ensure you boot into graphical mode

  systemctl set-default graphical.target

Step 4 - Reboot and enjoy

It is recommended that you log into the Plasma (X11)  vs Plasma (Wayland).  There are several non-critical wayland bugs.  These bugs are being addressed but aren't expected to be fixed until the RHEL 9.1 timeframe.

Troy Dawson

[1] - https://bugzilla.redhat.com/show_bug.cgi?id=2058657

[2] - https://docs.fedoraproject.org/en-US/epel/#_el9