Everybody's looking for a technical solution to a human problem. There's no COC, algorithm, policy, federation, whatever that will fix social media. The only thing that worked long-term where limited scoped* forums with 100% human moderation that basically had one single rule: "this is my forum and I appoint moderators that enforce my vision". You built long term reputation and relationships on these forums so whatever you posted was taken in context.
* limited scope = geographically, culturally, interests, numbers of people. But this of course will never make a billion dollar business.
So until people give up on the idea of the global app and return to "local" communities I don't think we're going to have decent social media.
EDIT: by local I don't mean subreddits, discord servers, etc, but the entire site/app to be local. Not a global with local divisions.