The question is too open. What type of modding are you looking for?
I'd like to modify existing units, and eventually add a couple new units and buildings. Ultimately I want to make a version that is dynamically balanced so that Alliance and Horde are more different from each other. I realize that starting from 0 that is a big project, so we'll see how it goes.
the best version is from this russian community, in https://en.war2.ru War2 Combat Edition
This is the only version that allows big modding capabilities compared to the very limited ways it had prior to 2020.
Good to know. Thank you, and thanks to Mistral as well.