Solo tracks in multitrack editor
To quickly solo tracks as expected, there are several ways to do that.

Click Solo button

Solo can be exclusive or non-exclusive, you may change the option in Mixspace preference page.
  • Ctrl + Click Solo to change the default behavior.
  • Alt + Click Solo to Clear Solo on all tracks.
Solo commands

Two commands are defined for track solo, you may set shortcuts for those commands to use them.
  • Mixspace > Solo Track.
  • Mixspace > Solo Track Exclusively.
Solo automatically

To automatically solo active track, you may choose Options > Solo Selected Track Automatically. 
When setting active track by following operations, the active track will be set to solo.
  • Left click on a track.
  • Left click on a lane in Mixer panel.
  • Change active track with keyboard shortcuts.