Not sure why you are bringing up the 1st Amendment.

Operating a social network app is not a protected form of free speech.

My concerns are largely over the precedent that might allow banning end-to-end encrypted apps over "national security," but there is an argument to be made on 1st Amendment grounds.

There are two 1A considerations here: whether an "app" is speech, and the speech of TikTok's users. If courts decide that TikTok is a "public forum," then there would be precedence to prevent the privation of this public forum in the interests of free speech. [1] On the other consideration, one of the landmark cases regarding software, Bernstein v. Department of Justice, ruled that code is speech, and this directly lead to the end of export control on encryption. [2] This has been further affirmed by a ruling in favor of the video game industry against a law banning the sale of games to minors in CA. [3]

[1] https://www.law.cornell.edu/supremecourt/text/482/569

[2] https://www.eff.org/press/archives/2008/04/21-40

[3] https://www.law.cornell.edu/supct/html/08-1448.ZS.html

This should be a top-level post. It saddens me the sheer number of people who accept the TikTok banning blindly because "national security" (not here so much but people I've talked to at work/other forums). This vague terminology could be adapted to encompass any communication that might be a threat to "national security" including encryption.

Once the precedent is set it will be damn near impossible to go back; just look at the Patriot Act.