Various projects on the open social web are working towards private data, whether that's @Mastodon getting funding for adding E2EE, Lemmy's upcoming 1.0 release featuring private communities, or Bluesky's work on expanding atproto with permissioned data.
Bounded communities with private data using open protocols sound quite like @matrix however.
I'm taking a closer look, as this comparison turns out to be quite a lot stranger than expected
https://connectedplaces.online/reports/fr163-decrypting-matrix/
