Odd but related question if anyone knows:

Are all preprints on arXiv public?

Or is there actually a private unlisted preprint queue?

From behavior I've observed, I'm guessing maybe authors have the ability to hide papers and send private invites for select peer-review?

> I'm guessing maybe authors have the ability to hide papers

No they do not.

In fact, authors cannot even delete submitted papers after they have officially appeared in the (approximately) daily cycle. You can update your paper with a new version (which happens frequently) or mark it as withdrawn (which happens rarely). But in either case all the old versions remain available.

Papers can be held my moderators, but as an author when you post you don't have the ability to hold or hide your paper.

Postings go up once a day as a batch, so you could wait 24ish hours to see your paper appear, longer if your posting is just before the weekend.