OK, I read the frikkin manual: https://github.com/tootsuite/mastodon/blob/master/docs/Using-Mastodon/User-guide.md#toot-privacy
“Unlisted toots are public, except that they do not appear in the public timelines or search results. They are visible to anyone following you and appear on your profile page to the public even without a Mastodon login.”
That’s some confusing language there. They’re public, but don’t show up in the public timeline?