Install alltray by entering the following commands in the terminal:
sudo apt update sudo apt install alltray
Description:
Dock any program into the system tray
With AllTray you can dock any application with no native tray icon (like Evolution, Thunderbird, Terminals) into the system tray. A high-light feature is that a click on the "close" button will minimize back to system tray. It works well with GNOME, KDE, Xfce 4*, Fluxbox* and WindowMaker*. (*) No drag 'n drop support. Enable with "-nm" option.
Homepage: http://alltray.trausch.us/
Version: 0.71b-1.1
Section: universe/x11