Let me say this right away – I believe that Ubisoft simply made this agreement to show how great their campaign is, how well-organized they are, and that even their license agreement is universal. But then they just ignored it because everyone doesn't care.

I googled Ubisoft's license agreement, and there are a couple of unpleasant points in what I found: https://store.steampowered.com/eula/298110_eula_0             https://legal.ubi.com/eula/ru-RU

Here, they say that we can be sued for mods that use their models.
And here, there is a very vague wording – they prohibit us from creating "derivatives" of the product – and this includes maps and mods.