Treating any communication platform that algorithmically selects which content to put in front of a user as a publisher, and legally responsible for that content, is the screamingly obvious solution that will deeply upset maybe seven companies and make life considerably better.
(This oped is psycho behavior)
A straight feed of what the user has chosen to follow: Not a publisher, carry on as you are.
Foisting all manner of shit into that feed and artificially boosting certain accounts/ opinions? Congratulations, you're bound by the same laws as The Sun. Better hire a lot of moderators, pronto.