The browser you are redirecting to or the website you want to visit is a custom in-app browser. Such browsers inject JavaScript code into each website, which allows Meta, the parent company of these platforms, to track you.
This means that if you click on a link on Facebook or Instagram to open another website, Meta is tracking you through that website.
Cyber security researcher Felix Krauss recently discovered this. According to him, their tracking code is inserted in every website link found in the Instagram and Facebook apps.
Such links are mostly found in advertisements. It works to send details like address, credit card number etc. to Meta along with personal details of the user.
His research focused on the iOS versions of Facebook and Instagram. In a conversation with The Guardian, Meta said that they have not misused the information and will not allow it to be misused.
Also read: While Using Facebook Other Websites Are Tracking You, How To Avoid?