I think both Friendica and Peertube don't support unlisted-like posts.

The Mastodon unlisted scope could be useful if you want to add a post that's visible to everybody even when not logged in, but you don't want to bother the global or local timelines with it. It is still sent to followers though, which may or may not be useful. The big problem with Mastodon's implementation is that I've heard these posts also don't show up in searches, not even with hashtags, which doesn't make any sense to me.

For Peertube I'm looking for a scope that's public locally, but is not public when federated out. In fact I believe this should be the default for any platform: don't show publically what you've only received from other servers.