Multi level menu columns
It is currently not possible since that is a multi level menu.
It is not recommended to use that kind of menu if you have too many second level items like this https://cln.sh/j1GT2PNw
Any one of those items can potentially have additional 3rd level sub-sub-menus so that is the principle on which the menu works, but each level should have no more than 10 items so it can extend laterally.
Maybe you can use a different menu type, try the "Mega Menu" dropdown, which is just a page builder essentially and you can add other menu modules in it, like the Catalog menu module from Journal > Modules > Catalog Menu... This module supports columns in auto grid mode, each column is a category which displays sub-sub categories as links.