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.
Tik tok are not a party to these communications, and they’re not a carrier or service provider. What they’re doing is wire tapping.
Lack of consent and lack of transparency, make this whole thing pretty messed up.
Are you possibly conflating tiktok tracking its own users within its app with somehow it gaining access to the OS itself and tracking users at that level? That is clearly not happening as far as what is publicly known as much as stories like this want you to believe for it to be the case.
What they do that is publicly known is not bad. Maybe there is something bad they're doing but these random HN top stories are not it. If NSA/US govt really wants us to avoid tiktok it needs better convincing than "omg they're stealing the x,y of your finger when you tap on an image."