They're not worried about CSAM. They worried about TikTok users being influenced during an election campaign.
And yes, it is a moderation issue. Specifically, the US doesn't want the current moderation team to be in charge of moderation.
Disclosure: I don’t use Facebook, Intagram, Twitter, nor TikTok
To put it in perspective, about a quarter of the US population uses TikTok. And politics are a major discussion point with the political content you're exposed to selected by an algorithm that is opaque and constantly changing.
It absolutely can be used to change the result of an election. And China has meddled in elections in the past (not least of all their own elections... but also foreign ones:
"China has been interfering with every single presidential election in Taiwan since 1996, either through military exercises, economic coercion, or cognitive warfare, including disinformation or the spread of conspiracies"
That would be easier to answer if we had a list of companies that can afford to buy it (that's a short list) and also willing to buy it (an even shorter list).
Sure - it obviously depends who buys it. Elon Musk, for example, would probably be a bad steward.
But what about Alphabet? That might not be so bad. As a fan of YouTube, I'd love to see the "shorts" feature killed off and all that content moved to a separate service where I can go the rest of my life without ever seeing a short repeating video.
Whoever buys it, it the US can force TikTok to be sold once, they can do it again if the buyer proves to also be problematic.