Install libayatana-appindicator3-1 by entering the following commands in the terminal:
sudo apt update sudo apt install libayatana-appindicator3-1
Description:
Ayatana Application Indicators (GTK-3+ version)
A library and indicator to take menus from applications and place them in the panel. . This package contains shared libraries to be used by applications compiled against GTK-3+.
Homepage: https://github.com/AyatanaIndicators/libayatana-appindicator
Version: 0.5.3-3
Section: universe/libs