Saw another post that had many great points. What if TikTok leaned into propaganda, topics like reunification with Taiwan? I promise that will effect us, big time.

Because China has interests that are in opposition to US interests, and they can sway US opinion any way they want by covertly manipulating the feed. They absolutely can do significant harm with this, including but not limited to selecting politicians, inciting chaos and political unrest, and even economic destabilization. I'm not sure that the US government actually has a much higher potential to do you harm than a foreign enemy of the US with a weapon like social media as you stated. You could make a strong argument that the political shitshow we are currently in is partially due to foreign interference through social media, and that is before they owned the actual platforms. The US government is not incentivized to destabilize itself at least.

probably because China is a foreign country and the US is (presumably) where you reside, and you should apparently trust your own government only. but i don't know exactly what a foreign government would want with your personal data anyways

I can insult Trump and Biden on social networks, travel to the US then travel back alive to my home country.

I wouldn't try that with China.

As an individual I’d rather be giving my data to China who probably have no interest in me personally, rather than a Five Eyes country who want my data to spy on me, and have more interest in persecuting me, stopping me at borders, etc.

Each country has the right to say if businesses or entities of a foreign country can operate in their borders. The US Govt is rarely directly involved with operationing a company or business, with the biggest exception being the US Postal Service. So while they might make rules and regulations for how companies can do business, these businesses are privately owned, what information they gather on clients or users is for commercial use, typically for advertising purposes.

With Chinese companies, this is not the case, even companies that are technically privately owned are heavily managed by the CCP if not directly operated or owned by an official member of the govt. So while in the US if a company like Instagram or Twitter was told by the US govt to hand over information about certain individuals, without a warrent clearly defining what data to hand over and the reason for it, those companies can and in the past repeatedly have used legal means to resist and deny those demands. This isn't a thing n China, and there is a lot of rumors that all the data these Chinese originating platforms collect by default goes to the Chinese govt, who can use it for anything from espionage, using insider information gathered illegally to manipulate markets or officials, to even things like blackmail or planning military actions in extreme cases. The CCP and all their associated companies have repeatedly shown in the past they don't care about the rights of citizens in other countries, copyright laws or intellectual rights, and would be more than happy to turn every teenagers smart phone into a listening device into peoples homes and tailor content shown to individuals they identified as someone they can manipulate to radicalize them in a manner that suits them without any regard to that persons wellbeing.

If you think the US Government is untrustworthy (which, yeah it's not) then you should be absolutely horrified at the thought of ever allowing the Chinese Govt and the CCP having access to any of your personal life or allowed to put software on your device and partake in a social network they curate and moderate.