Clear/Recall Solo    ⌃⌥⌘S

When tracks are soloed this command will clear the solo status for all of the soloed tracks. Issuing the command again recalls the solo state of each of the previously soloed tracks. Quick way to switch between “some” soloed tracks and “no soloed” tracks.

On the X-Touch you press and hold the OPTION key while clicking any SOLO button that is engaged. This command is also available in Logic Remote on the iPad and iPhone.

Solo tracks in a Logic Pro project — Apple Support

The first time any track in a project is soloed, a large Clear/Recall Solo button appears in the area above the track headers. You can quickly unsolo or resolo all soloed tracks using this button.