There is zero baggage on NOSTR regarding identities. An npub became the non-ambiguous way to reference anyone regardless of where they are writing from.

Thank you for the reference to that project called anproto, never had heard of it and I'm still without understanding what problem it really solves. Seems to encrypt texts but then contains zero outside metadata to route it somewhere. The website is very scarce on details for someone unfamiliar the scuttle-something they mention.