Same, I just looked around. Can’t seem to find anything relating to newsletters as a normal writer. I think it’s a publication-only thing. So, Substack/Revue’s space is technically not targeted here.

About the publication part, yes publications are basically shared spaces wherein multiple writers share around common theme or topic.
Individual accounts are only writers and there’s no “Publisher” term on this afaik.

They have a little about for publications here.