The article isn't complaining about in-app browsers per se, but that Instagram implements a special version of an in-app browser that injects Javascript code to

The article isn't complaining about in-app browsers per se, but that Instagram implements a special version of an in-app browser that injects Javascript code to track user behaviour. If you have noticed TikTok doing the same thing, please publish a blog post about it, and I expect it would get attention here on Hacker News, at least.