iOS Privacy: Instagram and Facebook can track anything you do on any website in their in-app browser
The iOS Instagram and Facebook app render all third party links and ads within their app using a custom in-app browser. This causes various risks for the user, with the host app being able to track every single interaction with external websites, from all form inputs like passwords and addresses, to every single tap.
https://krausefx.com/blog/ios-privacy-instagram-and-facebook-can-track-anything-you-do-on-any-website-in-their-in-app-browser