But Tiktok "is". At least Tiktok USA is registered in the US as a US corporation and therefore gets the same protections under US laws. Therefore constitutional protections apply.

You could say the owners of Tiktok don't necessarily get the same protections, but that's a different case. And in this case it is more similar to the Chinese Exclusion Act, but for business purposes rather than immigrational purposes, basically stating that Chinese people aren't allowed to own businesses that operate in the US, and must divest.