It literally can’t be private, just from the way Lenny works. You can’t have it all. You could in theory make it less visible, but that would be a false sense of privacy as it would be possible to do get the information with some effort. Just having it be fully open is more honest and makes no claims it can’t keep.

It’s social media, even if federated. On Facebook, tiktok or whatever they are also not private btw: maybe users can or can’t see them (I have no idea), but the company behind the platform certainly can and will use it for advertising to you and for what else to show you, making you the product.