I'm not absolutely certain it's the one you're referring to. However, it might be "AI Culture Conversion" which allows your vassals to prioritize cultural conversion. Forgive my late response.

Hey it may be silly to ask like that, but you said in some CK3 mod comment that you found a mod for dynamic cultural spread or protection. Could you send over the link, or at least share the name of this mod?

I hate n

*add inside joke here*

I thought he was joking

look at Saul M. Goodman's comment