I'm having this exact same problem. My macOS app builds and runs fine with Xcode 12.4 but produces Segmentation fault: 11 when I try 12.5.

I have encountered the same problem when I tried to post my app on the Mac App Store. I entered a BundleID in the format  com.icloud.appleID.AppName  and got the same message that it is not available.  I tried multiple variations of the AppName and got the same error message. I then tried entering a Bundle ID in the format AB123456C7.com.icloud.appleID.AppName where the AB123456C7 is the developer's Team ID, and IT WORKED.  It would have been great if the error messages had correctly indicated that it was a formatting issue and not the misleading not-available issue.

David, Is CodeBrain sufficiently advanced that it can process a command such as "Here is the Swift source code for my existing working app. Now make it run faster." Or, "Suggest ways to improve my existing Swift app."

This worked for me also. Thanks. I used: let groundGeometry = SCNFloor() groundGeometry.reflectivity = 0.1