The thing that has historically made a company bound to free speech is whether or not the government requires them to specifically search for certain types of infringing content. Coincidentally, this is the current legal framework that makes reporting images of child abuse legal: companies can voluntarily choose to to either not scan for CSAM, or can choose to scan for CSAM and must report it to NCMEC if they find any, and Apple is a prime example of a company that doesn't scan for it[0].
If the government is asking a company to go searching for specific otherwise legal content, that would be pretty good evidence for a court case to be made.
0: "Of all of the companies identified by NCMEC, I only saw one that had an unexpected decrease in reporting: Apple. According to NMEC, Apple submitted 205 reports in 2019 (a third my my reporting volume). Apple increased a little, to 265 in 2020, but then dropped in 2021 to only 160 reports. That's nearly a 22% decrease over two years!" https://www.hackerfactor.com/blog/index.php?/archives/955-NC...