No idea about the technical implementaion and how this md5 is generated or how it is used.
It's a legacy application which works as it is

Yup just pick the latest version of each map, thats exactly what the map manager does download & extract.

You can lookup the download path in the XML file: https://www.ugx-mods.com/downloads/manager/UMM.xml
Shouldn't be rocket science to find the download link [...

i dont think u can download the official ugx maps without using the ugx map manager to download those specific kinds of maps that r not on the website to download them on, not sure tho, cuz they have no links for it and only...