I have a question regarding a conspiracy theory I heard regarding Catholicism

Hey all! I have a genuine question. I have tried to do some digging on my own, but only came up with some weird fringe conspiracy sites. Obviously, this question is regarding a BS conspiracy rooted in some form of bigotry(?) But I can't find much about where this idea even originates from.

Someone told me the other day that they hate Catholicism because Mary mother of Jesus is, "the whore of Christ." I clarified, seeing if they were conflating Mary Magdelene with Mary, and they said no.

They claimed to be from a southern Christian tradition that taught the true gospel. But I'll be honest, I haven't heard this particular brand of crap.

Does anyone know where this conspiracy might originate from?