@Jon Thanks. I think I noticed that option in the past and I think I clicked it on and off a couple of times, not understanding its function (after all, it does not make appear any sort of subtle but visible area, suggesting its specific function for lasso-selection).
I still didn't get it at first, because I had my eyes on the column headers and I just saw a bit of a shifting, but the name in the first column simply remains in place - I saw no explicit indication that a special area has been aded, the area didn't stand out.
EDIT: I've now understood this is because I had adapted the default background color for all columns, giving them a light gray. Once I had reset the "unselected background" color to the original black, the lasso-selection area on the left suddenly became visible.
