The law wasn't rejected, the judge issued an injunction until the lawsuit is settled. Nor does the judge indicate he thinks this is blatantly a violation of the first amendment.

"That brings us to issues about First Amendment treatment of social-media providers that are not so clearly settled. The plaintiffs say, in effect, that they should be treated like any other speaker. The State says, in contrast, that social-media providers are more like common carriers, transporting information from one person to another much as a train transports people or products from one city to another. The truth is in the middle."

https://storage.courtlistener.com/recap/gov.uscourts.flnd.37...