A problem is that social media websites are simultaneously open platforms with Section 230 protections, and also publishers who have free speech rights. Those are contradictory, so which is it?
Perhaps @rottingleaf was speaking morally rather than legally. For example, I might say “I believe everyone in America should have access to healthcare”; if you respond “no, there is no right to healthcare” you would be right, but you missed my point. I was expressing an moral aspiration.
I think shadowbans are a bad mix of censorship and hard to detect. Morally, I believe they should be illegal. If a company wants to ban someone, they can be up front about it with a regular ban; make it clear what they are doing. To implement this legally, we could alter Section 230 protections so that they don’t apply to companies performing shadowbans.