To toggle enable/disable the “auto track selector” for all video tracks the shortcut is:
Option-F9 for Mac and Alt-F9 for Windows and Linux
For the audio tracks use:
Command-option-F9 and Ctrl-Alt-F9 for Windows. Be careful using this with Linux as it will switch your virtual terminal instead and your screen will go black (Use Ctrl-Alt-F1 or Ctrl-Alt-F2 to recover).
If your goal is to force a clip to land on a particular track, then you can skip the above and simple ALT-click (option-click) the “auto track selector” for the track you want to isolate. Repeatedly Alt-clicking the same auto track selector will toggle the inverse of the selection. This works for the locks and disable track buttons as well. This is a quick way to enable one track while simultaneously disabling all others (or the inverse of that by clicking twice).