We can debug with iOS 14.6 in Xcode 12.4. Go to this repo and download the iOS 14.6 package, then unzip Open the Applications, Right-click on Xcode 12.4, and click on Show Package Contents. Then, open the DeviceSupport folder by following this path "Developer > Platforms > iPhoneOS.platform" Drag your iOS 14.6 package to this folder, restart your Xcode and build. This solution worked well for me, and I hope it will work for you as well.

For my solution, I had changed the Flutter channel to Stable. Then, flutter clean -> pod install -> Clean Build Folder and Archive again. It worked well.