To translate the above into a useful feature:
You need to drag the vertical separator bar to the left more and more in small cuts until the preview panel no longer responds by growing larger.
See snaps
137 shows the cursor that has changed and is ready to be dragged left
139 shows the new tabs and a change of functionality: See the Queue: See the Job properties.
138 shows the preview panel in small size when the vertical separator is too far to the right.

Enjoy.

Fresd