As of Sunday, the commerce department has announced that TikTok and WeChat can no longer host a US App Store. This means that users can no longer download any of the apps.
Thereafter, TikTok will continue to work on the iPhone until November 12, when the Trump administration bans Internet traffic from the app unless a proposed agreement with Oracle is approved to alleviate national security.
The situation is more serious with WeChat, as the app no longer works in the US as of Sunday.
If you have downloaded TikTok before Sunday, the app will continue to work without any problems. But there will be no more security updates or bug fixes.