1. Expert opinion seems to be that the perceived threats indicated in the case of TikTok are vague and over hyped, and there is no concrete evidence produced.
2.Federal Government may not have sufficient authority to promulgate such a ban, even on grounds of national security. May be possible to squeeze out the cash flow of the company through trade restrictions, may be able to mandate that this app cannot be used by federal employees while on duty, may be even possible to disallow their usage on federal government premises, but it cannot ask Apple and Google to take an app down from the app stores.
3. If that is the case then we are moving into a government-licencing regime in the US, effectively. That is, you can have your app distributed only if you have the necessary license/authorization from fed government which can be revoked at any moment. I don't think that is the right direction. So to have such special powers for ostensibly national security purposes is undesirable and detrimental to the very system that US is claiming to champion.
The whole episode is wrapped up in a frenzy of reactionary whipped up paranoia that is reaching an alarming cacophony considering the commentary here.
This is obviously a nuanced matter, and needs to be approached as such, not with a coldwar-era Hollywood Manichaeian dualism.