In yesterday's decision in Missouri v. Biden, the Fifth Circuit (Judges Edith Clement, Jennifer Elrod, and Don Willett) held that the federal government violated the First Amendment by causing social media platforms to block posts on various topics (including "the COVID-19 lab-leak theory, pandemic lockdowns, vaccine side-effects, election fraud, and the Hunter Biden laptop story").
The court acknowledged that the First Amendment doesn't bar social media platforms from acting on their own to restrict user speech, since the First Amendment applies only to the government and not to private parties (including large corporations). But the court concluded that the First Amendment may be violated "when a private party is coerced or significantly encouraged by the government to such a degree that its 'choice'—which if made by the government would be unconstitutional—'must in law be deemed to be that of the State.' This is known as the close nexus test."
As to what constitutes "significant[] encouragement by the government" to restrict speech, the court held:
