Install cairo-dock-xfce-integration-plug-in by entering the following commands in the terminal:
sudo apt update sudo apt install cairo-dock-xfce-integration-plug-in
Xfce 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 Xfce environment. This is auto-activated, so you don't need to activate it.