(Since UberMenu 3.2.1)
You can create vertical dividers ( lines / borders ) between your submenu columns with the Submenu Column Dividers setting in the menu item settings. Remember, set this on the parent item to control the dividers in that item’s submenu
Select the color you’d like and this will add a 1px left border to the columns in your submenu.
Note that if your columns are different heights (since they contain different amounts of content), the borders will therefore also be different heights. To make sure your dividers are even, use the Submenu Columns Minimum Height setting and set the value to the height of your tallest column.