Free speech is a right that applies to citizens, not foreign governments.

I don't think the problem is that if/when it happens, it will be "undetectable". The issue is that if we have a polarized party-over-country political environment (which we do currently have), there is absolutely no guarantee a) that there will be a consensus about that the problem is real, that it matters, and that it should be addressed, b) that the party in power doesn't stand to benefit from interference and therefore takes no action, and c) we will have eyes looking at this seriously before it is "too late".

Protecting free speech of geopolitical competitors (China) and their economic agents (TikTok) is legitimate avenue for democratic destabilization.

It seems to me that democratic destabilization in US is already in full swing and has nothing to do with TikTok subtly changing youth opinions.

The issue isn't whether TikTok is currently doing it or no, its whether this is a national security risk in the future, which is absolutely is. I think he's an idiot and he's using the issue to distract from Russian interference, but its a concern that if you only wait to address this _after_ its already a problem, it will already be unaddressable for the reasons enumerated in my comment.

But it might have something to do with Facebook advertisement paid by whoever pays more.