@0x1C3B00DA Our working understanding right now will treat the "unlisted" visibility level as a Mastodon-only quirk that has no meaning in #nodebb. Will update with more info re: post ACLs as we develop.
#Mastodon supports mentioned-only which is unintentionally leaky (one errant mention and the jig is up). We intend to fully de-couple mentions from the ACL, so you can mention anybody you want, but that doesn't change the ACL if you restrict visibility to certain people.