Bitten by this today; spent all morning trying to debug issue using remote devices in the hands of testers and some AWS Device Farm instances.
If I implement a view that has a conditional check for iOS 15 or newer, my iOS 14 release builds crash when the parent view includes the implemented view.
In order to avoid the crash, I've had to implement two versions of my view - an iOS15+ View and and "older" view. I then use a conditional check in the parent view to determine which of the two subviews to call.
Not great, but at least it stops things from crashing.