Created attachment 144209 [details] Scroll bar appear for little space at bottom All elements are visible but the scroll bar in categories list appears and has no usage at all. See attached image for more info.
All elements are *not* fully visible; the list item for "Help Center" cannot be fully displayed. That's why there's a scrollbar. The text may be visible, but the full height of the list item is taller than the text. That said, I can see how this would be visually annoying. It might be worth tweaking the code so that the menu's height always results in the list area having a height tall enough to accommodate an integer number of list items.
This is mooted by the changes in Plasma 5.26 to make the popup resizable, so now you can make it perfectly able to accommodate as many list items as you want without scrolling, no matter what font or font size you use. The only remaining issue would be to make it do this by default, which doesn't have a high enough reward-to-effort ratio methinks. Closing, sorry. :)