Problem Solved
Fix (edit DefaultEngine.ini under [Mac]):
EditorDefaultArchitecture=MacTargetArchitectureHost DefaultArchitecture=MacTargetArchitectureHost
SDK/Xcode note:
I also hit packaging issues related to the SDK. I fixed them by installing Xcode 16.4 (I had been using 26.0.1). Make sure your Xcode version and SDKs match the engine.