Volume icon is lightweight volume control for the system tray.
It is installed but disabled by default in Mabox, because there are other ways to control sound volume configured:
- Super+V is a key bind for pavucontrol
- multimedia keys XF86AudioRaiseVolume and XF86AudioLowerVolume are preconfigured and should work
If you like to enable Volume Icon use XDG Autostart Editor: Main menu -> Mabox Config -> Autostart -> Choose apps/services (GUI editor) to enable it.