Install libappindicator0.1-cil by entering the following commands in the terminal:
sudo apt update sudo apt install libappindicator0.1-cil
Description:
CLI bindings for libappindicator
This package provides the appindicator-sharp assembly that allows CLI (.NET) programs to take menus from applications and place them in the panel. . This package contains assemblies to be used by applications.
Homepage: https://launchpad.net/libappindicator
Version: 12.10.1+18.04.20180322.1-0ubuntu1
Section: universe/cli-mono