I'm not sure if they're used anywhere, but private mutes exist. I could see people wanting more privacy forbtheir social graph, that's really some of the most delicate information we have.

they would just be private events encrypted to the user themselves that contain follow lists i don't see any reason why not to do them or how it really harms what people are happy to make public the price of many commodities and equities on exchanges have "dark pools" too, people sometimes have reasons for this, but if they interact with their hidden follows they are gonna leak it anyway

There's a tension there, because the social graph is the most game-changing element of Nostr. Nostr as the social layer of the whole Internet is a largely untapped potential, and private follows obviously limit some of that potential. If all social graph data is private, then a large chunk of the Nostr value proposition disappears, IMO. However, allowing users some discretion would be good.