First amendment rights are only granted to US citizens (and presumably US companies).
There are many examples of import embargoes.
There are many examples of import embargoes.
It would be simple to prove that TikTok (and it's parent company ByteDance) are free from foreign government involvements by simply disclosing their worldwide finances and having external auditors confirm they aren't receiving payments from adversaries.
I don't see why the company would prefer to face a potential ban from it's most lucrative market rather than go that route...