https://www.theregister.co.uk/2019/11/12/facebook_camera_bug/

Facebook’s iPhone app has a new feature – and one that netizens aren't too happy about: it opens the phone’s camera app in the background without your knowledge.

A number of users have noticed the unusual behavior and posted videos demonstrating it. In each, the rear camera is clearly turned on and can be seen behind the main app screen: something that is unnecessary and the user is not informed about.