You're writing as if this is just analytics tracking a user's actions in their own UI. It's not! This is tracking actions users take, and data users enter, on 3rd-party websites.
That is not "what happens in Tiktok's app," as you put it in your reply. It may be hosted "in" the app in a technical sense, but the typical user who is fullscreen viewing a totally different website may not feel like they are "in" the app at all. I wouldn't bet that most users even get that there's a distinction between an in-app browser vs. opening a tab in the main OS browser (on Android at least, the back gesture takes you back to the app either way). Users almost certainly doesn't expect the original app to be able to read passwords and other text that they type on those 3rd-party sites.
And how do we know Instagram and yelp are not doing something similar? If you have in app browser you can track user activity much more invasively. That’s not an argument against tiktok, that’s an argument against in app browsers. If you’re so concerned with user privacy ask Apple to remove that functionality from all apps instead of slyfully picking and choosing the apps to attack.
That is not "what happens in Tiktok's app," as you put it in your reply. It may be hosted "in" the app in a technical sense, but the typical user who is fullscreen viewing a totally different website may not feel like they are "in" the app at all. I wouldn't bet that most users even get that there's a distinction between an in-app browser vs. opening a tab in the main OS browser (on Android at least, the back gesture takes you back to the app either way). Users almost certainly doesn't expect the original app to be able to read passwords and other text that they type on those 3rd-party sites.