Nostr doesn't do a whole lot to protect your privacy at the protocol level. Your npub is public proof that every event you sign was signed by the same person or someone they authorized, unless they got your keys stolen, but whether it can be attached to you depends on your opsec. Relays are allowed to share your events freely to everyone, but they're also allowed to restrict access however they see fit. Encryption schema used for things like end to end encrypted chats are still not as private as competing non-nostr services, but advancements are being formalized so they can be put into use. Ultimately, the privacy nostr affords people will largely depend on how the software is built on top of it. Decentralization will provide a degree of protection, and a much appreciated one, but without stronger protections built into the protocol, it still depends on how we use it.