The thing about telling teenagers (who are the primary users of Tiktok at least) that something is now forbidden, is this will make even those not that interested before more likely go and download it before it gets banned. As how many US teenagers give a shit if there lip sync videos are being monitored by the Chinese/.
As for not allowing US based app store to host them or provide updated, If i were Bytedance or Tencent I would push out an update to the apps today to allow update from there own servers before they get booted off Google Play and Apple app store. They code do it via some hidden code just like Epic did to enable their in app payments after Apple had approved the app.