Long ago there was this thing called foaf https://en.wikipedia.org/wiki/FOAF and also https://en.wikipedia.org/wiki/Pingback ... it was the closest I've seen to completely decentralised social media.

Webmention is the modern counterpart: https://indieweb.org/Webmention

(The IndieWeb wiki is probably the best resource for exploring the personal website-based social networking tech nowadays. I recommend the author check it out and maybe iterate on that instead :)