There is a really big thread on Apple‘s forum about similar, Snapchat and instagram (not much re FB). Lots of emotion. Specifically its about the front (selfie) camera. And, pics and videos taken Within the IG, SC apps. Even worse when they zoom. Majority complaints re 11 Pro (So don’t get a pro to fix your issue, it will make it worse)
They blame the phone‘s camera, and Apple. The front camera on iPhones does not zoom natively, never has. Any Zooming, and image processing including the significant compression these apps do, is done by the app....not by iOS. Not surprising worst complaints re 11 Pro. It’s 12 MP front camera is 2x the resolution of any previouse iPhone, this probably caught IG an SC unprepared.
These are IG, SC, and possibly FB app issues, for them to fix in their apps...not iPhone 11 or 11 pro camera problem.