I don't think this practice violates the NAP under a traditional libertarian point of view, but it certainly is an example of coercion. I don't find the non-aggression principle particularly useful (like, ever, really). In this case, it's too easy of an excuse to say nobody is forcing you to use Discord (et. al), and they have a right to set their own terms of service. You could say no and take your "business" elsewhere. Under a libertarian framework, Discord has just as much of a right to do as they wish as you do.

The problem with the non-aggression principle is that it kind of assumes that everyone is a peer. It doesn't consider systemic or economic power at all really. It externalizes scarcity and says as long as I don't personally harm you, I can sit on my horde of bread while you starve and YOU would be at fault if you tried to do anything about it other than enter into some sort of contract with me where I hold all the leverage. It exists in an idealistic world where if one is not happy with a company or institution, they can frictionlessly create a superior alternative, or that one will materialize out of the ether due to market forces. Instead of considering that maybe such firms and institutions should be coerced to serve a public good instead of playing this market game where billions of people vote with their feet change social media platforms every week, every time one of them changes their privacy policy.

These companies take advantage of their monopoly power to impose their will upon and exploit their users. While social media companies aren't exclusive monopolies in the sense of the Bell Telephone Company, there is only one place you can go to participate in "Celestecord" or the Kerbal Space Program Realistic Progression Mod chat, or countless other examples. These companies know this. They know they can use the threat of cutting you off from you friends / community to force you to hand over information that you wouldn't surrender voluntarily. They know they can use this power to crack down on anybody reverse-engineering the protocol and creating third-party clients with fewer built-in surveillance and advertising features, or to prohibit people from implementing enhanced security features like end-to-end encryption.