When scrolling through the menu items using arrow keys, the background highlighting is not displayed on items having sub-menus using the Dark Theme UI.
In this example, we see the background clearly on Create Jump. Using the down-arrow key to go to the next item (which has a sub-menu), the background for Set Type and Set Tags is not visible, so one isn't sure where one is. This is the case for all menu items having sub-menus in Dark Mode only (e.g., File, Utilities).
TheBrain 10.0.17.0 beta / 9.1.x / 18.104.22.168 / (PB) 6 || Win7