Status icon on Gnome - kozec/sc-controller GitHub Wiki

Since version 3.26, Gnome support for status icons is broken. If you wish to enable status icon, minimizing to status icon or starting hidden, you'll have to install additional packages and extensions:

• libappindicator-gtk3 package (installed by default on some distros, especially Ubuntu-based)
• topicons extension to display icons
• appindicator-support extension to add support for AppIndicator protocol

Then add following line at end of your ~/.profile file and log out or restart your computer to apply change:

export STATUS_BACKEND=AppIndicator