He did violate their IP, just not with the mod itself but the advertising / his posts - at least in my uneducated opinion.

Take these examples:

https://archive.is/xKCtk https://archive.is/bfg53

He's using their IP to advertise his commercial product - a paid mod that supports their game. This use of IP generally isn't considered fair use. It's not the fact that it supports the game that's a violation, it was the advertising that was more my point.

And then as DMCAs generally go, companies overreact (like Patreon) and overreach. I don't think CD Project Red could reasonably have done anything if all this was was a footnote that his mod supports CP2077 and the advertising was happening via content creators plugging it - or otherwise off Patreon. But because he happens to use their IP to advertise directly, this was the outcome.

I'm not a lawyer though, there is probably more at play here.