Native Camera App
Is there a setting for the camera app to allow for flip from the front facing camera to the rear camera during a live video?
iPhone 12 Pro, iOS 15
Not sure.
Some can switch; while I hadn't checked.
And have little experience of merit, with any advanced features.
(decades of manual film and processing experience; w/ 35mm)
There are a few appear to say they do that; whether or not 'native', can't say:
https://duckduckgo.com/?t=ffab&q=front+to+back+camera+while+live+iPhone&ia=web
Some had suggested video won't do it; or used to, in older version iOS/iPhone.
https://duckduckgo.com/?q=front+to+back+camera+switch+in+iOS+while+live+iPhone&t=ffab&ia=web
Could could work; or maybe with an App;
..And of those I've skimmed through, features can be costly extras..
Maybe others can add substantially to the lists, found by search?