Cal Newport makes a point about how in the early days of Facebook, it was essentially mirroring your real world social network. In fact, I remember how fun and innocent Facebook was in its early days.
Perhaps the biggest shift in Facebook's evolution is towards algorithmic feed optimisation and expansion into more public areas that exceed dunbar's number.
Scuttlebutt (https://scuttlebutt.nz/) avoids this shift in its design by doing away with the "global singleton" network that Facebook, Instagram and other have.
Another interesting project that is bringing back self-sovreign identity is Bluesky's At protocol (https://atproto.com/) which also make the "algorithm" part of a feed open source.
Some building blocks that are worth considering: IPFS/IPLD (https://ipfs.tech/) and Hypercore (https://hypercore-protocol.org/).
Disclaimer: I work full time on IPFS