I feel like they've got a strong constitutional case. One BBC article I read said that 60% of their company ownership is by global hedge funds so they just plainly aren't a Chinese company. Singling them out for having dissident information through an act of congress is precisely what the 1st Amendment is supposed to protect against. With the sale supposed to happen in November at the earliest, the red scare will either fade by then or become a much larger issue they can capitalise on.
The constitution means jack shit, it wouldn’t matter if it explicitly stated “TikTok shall not be banned”, the state does whatever the fuck it wants and the hardest part is coming up with the weasel words in the judgement that explains how it’s perfectly constitutional, ackshually.
I'm not an expert on US law, but singling them out like this via legislation smells a whole lot like a bill of attainder, which is banned under Article 1 (not the First Amendment, though that's definitely relevant also) of the Constitution.