Since all Formal Objections must be made public, isn't that saying the resolution must be public?

Yes, it's saying that. But to me, it's also saying that you should make the announcement not just with the same confidentiality, but also with the same visibility. E.g.: If the FO is announced on a well-read mailing list, the resolution needs to be announced there too. Putting it on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying ‘Beware of the Leopard.” [1] doesn't count, even if the cabinet is not designated as confidential.

[1] in case this example looks a bit over the top to anyone, it's a quote from a novel: https://www.goodreads.com/quotes/40705-but-the-plans-were-on-display-on-display-i-eventually

Unless there is new information by December 20, this pull request will get merged.