Except it is. The Supreme Court has actually ruled that the First Amendment rights for Americans to receive foreign propaganda, even during the Cold War:

https://firstamendment.mtsu.edu/article/lamont-v-postmaster-...

I don't think you know what the First Amendment is. Not only does it guarantee freedom of expression, but also freedom to receive other's expression and speech.

The U.S. government is not allowed to ban any foreign books, movies, or even propaganda.

I really wish people like you do a little bit research before making such a confident statement like that.

They may not legally be allowed to ban it, but that doesn't mean it has to be easy to access it. This is probably also why banning Tiktok was / is such a challenge and couldn't just be done with Trump's exective order after Zucc whispered it in his ear in 2019, and why they can't just block it, but have to subpoena the app stores to delist it.