In older versions of UE, you could customize the menus in the Menu Bar. It's been a couple of years since I used UE on Windows, and I don't see this option anymore. Was it removed?
Yes, there have been changes in the last two years.
There is since UE for Windows v23.00 the ribbon mode which is customizable. But it is possible only to add ribbon tabs and ribbon groups and add there the commands of your choice. It is not possible to modify persistent the predefined tabs and groups. For example a ribbon tab for user/project tools can be added. The ribbon customization dialog can be opened by right clicking on the ribbon and left clicking on context menu on appropriate context menu item.
Then there is the toolbar/menu mode with contemporary menus. This is the ribbon structure displayed as classic menu. A ribbon tab is a main menu. A popup menu in ribbon mode (the menu opening on clicking on a down arrow symbol right of or below an item on a ribbon tab) is a submenu in contemporary menu mode. It is not possible to customize the contemporary main menu. For this customization a temporary switch to ribbon mode must be made to customize the ribbon getting displayed after switching back to contemporary menu.
With UE for Windows v23.20 the traditional menus have been reimplemented for users like me which favor toolbar/menu mode with the well known menu structure of UltraEdit versions prior 23.00. The traditional menu is up to version 24.10 not customizable.
Customizable are the document window and file tab context menus and the toolbars in both toolbar/menu modes.
So ribbon tab and contemporary main menu are partly customizable and partly predefined and the traditional main menu is not customizable at all.