[chasil]

As I understand it, TikTok is only being removed from the Apple & Google app stores, and existing installations will not be touched.

For Google, sideloading TikTok remains an option, both for new installs and updates. This is not an option for Apple.

Is there a point where the installed app itself becomes illegal?

[monocasa]

If they have a ban, they can force ISPs to block it. The app does nothing without server access.