Install wmsystemtray by entering the following commands in the terminal:
sudo apt update sudo apt install wmsystemtray
Description:
Freedesktop.org system tray as a Window Maker dock app
wmsystemtray is a system tray using the freedesktop.org system tray protocol designed as a Window Maker dock app. It has the ability to display more than one dock window to make room for more tray icons, and the ability to scroll through the icons if more are present than will fit.
Homepage: http://sourceforge.net/projects/wmsystemtray/
Version: 1.4+git20150508-2build1
Section: universe/utils