I think what they are saying is the government cannot collude with private firms to restrict Constitutional rights.
There certainly is collusion between the Deep state and the Tech Oligarchs.
All of them colluded against President Trump.
“which not only permits tech companies to censor constitutionally protected speech but immunizes them from liability if they do so.”
I still think it doesn’t apply. They are not a government entity so how can someone sue them for that? The first amendment doesn’t apply to them.