I can't compile my mac catalyst app with the new SwiftUI life cycle on Big Sur with the final Xcode 12 release. The deployment targets for Big Sur are missing. This issue isn't present in Beta 6.
macOS Deployment Target 10.16 or 11.0 missing from Xcode 12 App Store release
Quoting the Xcode 12 GM download blurb:
"For development on macOS Big Sur or to support Apple silicon, continue to use Xcode 12 beta 6."
"For development on macOS Big Sur or to support Apple silicon, continue to use Xcode 12 beta 6."