Private small self run social media already exists. It's personal Minecraft servers.
When I was younger I ran a Minecraft server out of my toaster of a PC. Friends hopped on, made their own little houses, built stuff and talked. Friends would pass in and out and in order to get in you had to be invited! I'd say max there were 10-20 people on there somewhat consistently.
It was great, and better than social media or even game for hanging out with your friends IMO because it emulated synchronous human interaction instead of just setting up feeds where everything has to be "perfect".
It was easy enough for a 14 year old to setup, and administer. Mods made it hackable and fun.
I guess the metaverse was already a thing back then huh?