Installing KDE on Rocky Linux 9 is easy, as long as you enable the right repositories. One of these have changed since Rocky Linux 8, so if you’ve found a RL8 guide online, you may have been stymied.
Install Rocky Linux and choose either Server with GUI or Workstation under software selection.
Make sure the account you created for yourself is an administrator.
After installation has completed, log in and open up a terminal app.
Add the EPEL Repository
sudo dnf -y install epel-release
PowerTools is now called CRB. This repository has many of the prerequisites that KDE needs.
sudo dnf config-manager --set-enabled crb
Update packages with the new repositories
sudo dnf -y update
Install KDE Plasma
sudo dnf group -y install "KDE Plasma Workspaces"
Disable the GNOME login screen an enable the KDE login screen
sudo systemctl disable gdm
sudo systemctl enable sddm
Once you reboot, you should be at the KDE login screen.
Make sure to choose Desktop Session: Plasma (X11) or Plasma (Wayland) from the login screen.
Enjoy KDE Plasma on Rocky Linux 9!