This isn't about privacy; it's about who gets to promote what ideas to Americans. Do you think that a post about Tienanmen Square, about Uyghur persecution, or about Taiwanese independence, will get nearly as far on a Chinese controlled media platform?
Because the Chinese Communist Part is not stupid enough to just exploit their leverage over sovereign nations for shits and giggles. You don't need a smoking gun to understand how corporations in China operate. They operate with the blessing of the CCP, and regardless of whether they've ever done anything, the scale of what they could do if they wanted to would be some spectacular lessons in modern propaganda.
This is simply more of the same fearmongering we’ve heard before. Not an answer to their question.
The fear is justified though. We fix security holes because they are security holes, not because they have been exploited before.
Seconding this: you don't try and fix things after the damage has been done, you try and anticipate _where_ and _when_ the damage could be done. In this case, giving a foreign _adversarial_ (<- emphasis) government significant leverage over citizen sentiment is a massive security hole.