Monitor in Portrait Mode; How to Scroll Horizontally/Increase Main Column Width?

Hello,

My Monitor is in Portrait Mode (Tilted to Vertical position) ; So… since I have Outlines with lot of nested levels, I would need to Scroll Horizontally/Increase main column width to see all my stuff. Currently, the deeply nested levels are quite squeezed.

How can I do that?

The easiest way would be to temporarily add another column and then make the outline column wider by dragging the divider between the column titles.