Addictivetips published a tutorial about sending Spotify to the system tray on Linux.

How to send Spotify to the system tray on Linux

Although Spotify is available on Linux, it does not support the feature that other platforms have where it is possible to send the Spotify app to the system tray, out of sight. Sadly, the Spotify developers haven’t added this feature to the Linux version of the app, and there’s no way of knowing if it will ever come.

How to send Spotify to the system tray on Linux