It’s not a certain company, it’s a whole class of them (partially defined by POTUS’ whims)
Sure, the government can do that, and when doing so infringes on Americans’ speech or access to information, it introduces First Amendment questions that must be addressed.
“The government says CNN can’t post stories from BBC” isn’t immediately resolved by “it’s a foreign company.”
It sounds like you're saying that there's some content on TikTok that Instagram Reels/YouTube Shorts/etc. won't allow on their platforms. Is that correct? If so, can you give an example?
No, and no one is saying they can. The law says American companies can't do business with a certain foreign-owned company.
It is beyond settled in law that this is something that the US government can do.