The US need not restrict any of your speech. You’re not directly communicating with any of TikTok’s users when you post to it, TikTok is. In the Internet age, even apparent one-way communication is handshakes upon handshakes. Consider this: You’re free to send whatever messages you want to ByteDance. They’re just not allowed to reply (or have anyone reply on their behalf). The app is a useless binary blob if it can’t set up a TLS connection.