But again, you can make that argument about any platform or medium where speech can be posted or displayed. If the department of public health condemns a local movie theater where I host indie movie screenings, that is not a violation of my first amendment rights because they are not prohibiting my ability to make or share content, they are simply removing the space it is currently shared. If that comes out to the same effect for some people who are all-in on TikTok to the exclusion of any other short-form video sharing service, sure, maybe there are grievances. But that still ends up being a self-imposition made by the individual at the end of the day.
Not to mention, the US government is not trying to close down TikTok. They are prohibiting the owners of TikTok from doing business in the US. The company itself would be the one to make the decision to close the service rather than sell it off, so unless the fed is going to force a private business to keep itself open to placate the masses, it’s a decision made by a private company outside of any constitutional law.