Install cairo-dock-gmenu-plug-in by entering the following commands in the terminal:
sudo apt update sudo apt install cairo-dock-gmenu-plug-in
GMenu plug-in for Cairo-dock
A collection of official plug-ins and applets for cairo-dock. . Displays the common Applications menu and the Recently used files. This is compatible with any XDG compliant menu (GNOME, Xfce, KDE, ...).