@Stan_Smida Try with the Xcode 13.3 beta. There have been a number of weird, iOS 14 + release build only crashes reported on these forums, at least some of which are fixed in Xcode 13.3.
I ran into a very, very similar issue in __swift_instantiateConcreteTypeFromMangledName using SwiftUI + #available. This person also ran into one in swift::ResolveAsSymbolicReference::operator (which also appears to be related to demangling + SwiftUI + #available) and then there's this one which had something to do with concurrency.
Until you can actually build a release using Xcode 13.3, you can try this workaround from the above-linked developer forums thread. Something similar worked for me & this way you don't have to set @_optimize(none).