Install ayatana-indicator-application by entering the following commands in the terminal:
sudo apt update sudo apt install ayatana-indicator-application
Ayatana Application Indicators
An indicator to take menus from external applications and place them in the panel. . The application supporting indicator based panel applets provides its menu tree via the DBus bus org.kde.StatusNotifierWatcher. . This version of application indicators accepts connections from any application built against either of the available indicator frameworks: Ayatana Indicators and Ubuntu Indicators.