Hi,
After no answer from that first topic KDE Menu Editor missing application & using directory structure, I made a small program to help making a start menu with LegacyDir option. Basically, it scan & copy all .desktop files inside a directory then you can make your own directory structure & move these files into it.
Because i don’t find anything like that, here is the github in case of :
GitHub - FroggyCorp/xdg_legacy_dir_menu_maker
Feel free to report problem 