If decentralized networks strike your interest, also look into Anonet, DN42, IRC, UUCP and Usenet. (Not all things on this list are still operable)
Thanks! Actually this current rabbit-hole side quest was sparked by a arc of nostalgia around 90s IRC. Download a client, joint chat rooms and just chat. Anything like that today? No setup required.
IRC is still around - and more popular than Usenet. Go and connect to Libera and see which channels exist. Or Rizon, if you're more of a 4chan guy.