Try other apps with cameras and see of they do the same thing. I know you said the stock camera app is fine but just to get more to compare it to. Could be a issue with the Tik Tok app itself and how its behaving when interacting with your phone. If you have another device, try the Tik Tok app on said device and see if it behaves the same way. I know this wont help you fix it but it would help you isolate the problem to only your current phone, especially since a reinstall didnt help.

I would say its specifically something with the TikTok app and how it interacts with your device. Only things I can say is contact TikTok themselves, reinstall the app and delete all residual data on your phone when doing it, make sure the app and your phone are as up to date as possible, or if you're really wanting the app then see if a factory reset does anything.

It almost looks like it is recording the light sources and what is in focus. My Sony RX10 camera has an option to use a mode like that so you can tell what is in focus and what is not.