I’ve merged this with the bug report for this issue. What you found before was something else, surely, as this only recently came up as the result of trying to fix another problem with how scroll views were suddenly changed a couple of months ago.
This button has always been the superior option to use if you want to make a number of changes to columns at once, as it opens a semi-persistent popover that you can check boxes on and off in. So it’s definitely not removed on purpose.