dansup, they're only sent to followers, but anyone could fetch them by direct link. They have an extra `target` field with the wall collection, and are addressed to as:Public (and group's followers in my case, not sure if that's necessary). Crucially, they aren't addressed to the user's own followers. When you post, you first send a Create{Note} to the group's inbox, then the group actor sends an Add activity to followers saying that it added the post to its wall collection. It works exactly like Announce{Note} otherwise. It's in my FEP that you probably already know about: https://git.activitypub.dev/ActivityPubDev/Fediverse-Enhancement-Proposals/src/commit/f94077e1514928c2d2ae79d86a5953c93874b73d/feps/fep-400e.md

I currently don't have private anything because I'm kinda reluctant about it. In a decentralized system, privacy on viewing something would basically rely on any server admins involved not looking into their databases. But apparently there is a demand for this anyway, so I could add private (or "closed", in VK terms) groups at some point. Need invitations first tho.