I don't see the downside to Americans as a result of this. Meanwhile, China lost a valuable propaganda tool.
Or, would have. It's all a moot point now that the appeal to Trump's ego worked.
The downside is mostly in terms of PR. But I agree that Americans and American media would still probably call any foreign ban on Facebook or youtube "censorship". Or would say that Chinese style bans on foreign social media is wrong - except when they do it. So I guess I agree, there's no big downside for Americans.
They are just shifting to one propaganda tool (tiktok) to another (fb). For the american citizen nothing changes.