I could not find a post on this thread that reports an issue with selfies taken with iOS native camera app. Therefore, no evidence of concern in this thread re iPhone 11 pro selfie camera problem.
The selfie camera on this phone is by far the best resolution (12MP) ever on an iPhone, by almost 2x vs. last year.
The selfie camera has no optical zoom capability, never has had. The native iOS camera app has no digital (software) zoom capability either, never has had.
The issues being reported, while real, are related to bug(s) in the 3rd party apps (they are specific to the new phone). Not with the iPhone selfie camera itself, or with iOS. Those 3rd apps are doing all the (digital) zooming, the final image processing, and compressing to manageable file size.
With the large increase in resolution of the selfie camera on this phone (with corresponding large increase in per photo data requiring processing), it is not surprising that many 3rd party apps were initially not ready to handle it well.
Good news is, because of the new very high resolution selfie camera, when those apps finally get it right, the selfie photos taken with them should be the best you’ve ever seen on those apps.
Also, if issue with selfie photos only occurs on 3rd party social media app, there is zero chance that exchange for a replacement phone will fix.