As the Moody v. NetChoice majority noted, the parties focused on Facebook's and YouTube's main feeds. The majority similarly focused on those main feeds in its extensive discussion of First Amendment principles, and, as co-blogger Ilya notes, it left little doubt about the unconstitutionality of the Texas and Florida statutes as applied to them. NetChoice didn't invalidate the laws on their face because of uncertainty about how the statutes apply to other services that were barely discussed (if at all) in the briefing below.
The article that co-blogger Eugene links to in his 12:19pm post today made probably the strongest argument in favor of the Texas and Florida laws at issue in NetChoice (and both states' lawyers cited Eugene's article in their oral arguments): that platforms can be treated like common carriers such that the regulation of the hosting of users does not implicate the First Amendment. The Alito opinion (concurring in the decision to remand but rejecting the majority's application of the First Amendment to the statutes as issue) largely agreed with Eugene's reasoning, but the majority did not.
Eugene says that "the majority did not decide whether the First Amendment extends to platforms' many other functions—such as platforms' decisions whether to 'deplatform' users in a way that keeps readers from seeing the user's posts even when they deliberately seek out those posts," and I think that's correct for platforms other than the curated ones like Facebook's and YouTube's main feeds. I could easily imagine that the Court might find that some platform like Gmail cannot deplatform anyone based on their viewpoint, on the theory that Gmail does not engage in expression for First Amendment purposes. But Texas and Florida did not enact these statutes to quash Gmail's exclusion of users based on their viewpoint.
