Install cairo-dock-kde-integration-plug-in by entering the following commands in the terminal:
sudo apt update sudo apt install cairo-dock-kde-integration-plug-in
KDE integration plug-in for Cairo-dock
A collection of official plug-ins and applets for cairo-dock. . This plug-in provides functions for a better integration into the KDE environment. This is auto-activated, so you don't need to activate it. It is designed for KDE4.