That would make it a moderated ecosystem, not a closed one. AFAIK, Section 230 protection extends to online advertisement as these companies claim the ads are

That would make it a moderated ecosystem, not a closed one. AFAIK, Section 230 protection extends to online advertisement as these companies claim the ads are user generated content. There were many law suits against Google and Meta about being responsible for the content and ads their algorithms push and how it radicalized people or harmed people. I recall Google and Meta won all those cases. Plus, in the 1960s there was a famous Supreme Court case against NYT for publishing a pro-civil rights ads that contained wrong claims against some like cop or politician in the south. They argues that NYT was libel for the malicious attack. The Supreme Court ruled in NYT favor because even if the ad buyers were malicious, they need to prove that NYT was also intentionally malicious in their intent