This toolbar includes all settings of Drupal 8 Mega Menu, just select menu then configure. There are many many level of configuration: submenu setting, column setting and menu item setting.
This allows you to configure each link you added in the Drupal core menu. You can: add block, have it styled by adding extra class, set icon (Bootstrap icons) and add description.
Contains all the level 2+ items. Allows you to: add and remove row, set the submenu’s position, have it styled, edit its width...
Allows you to: add and remove column, set grid, add block to column and style the column with extra class