Did you connect the NCF core? Or did you just dump the files into a folder? You also need to modify the executable, expand the lists, and assign unique IDs to the new creatures.
https://heroes5.fandom.com/wiki/New_...rk_(NCF)
I just dumped the files into a folder. I took a mod that changes the Academy Castle into a Conflux as a base, removed everything that changed the Castle itself, and edited the creature files, detaching them from the Castle and returning them to the neutral faction.
I looked at your link about the New Creature Structure. I don't understand at all what needs to be done there, what exactly to download, and how to work with it. As far as I understand, I need to download something from here: https://github.com/Might-Magic-Heroes-5-5/MMH55/blob/master/Frameworks/NewCreatureFramework/NewCreatureFramework.yml
I don't understand what this yml file extension is.