I have an Objective-C MacOS app originally developed in Catalina on a 2012 Macbook Pro and recently ported to a 2019 MacBook Pro running Monterey and using Xcode 13.4 in response the App Store no longer accepting apps developed in Xcode 12, which is the newest version supported by Catalina. The app is targeting MacOS 12.0 (Catalina). The app builds and runs OK on Monterey, but when run on Catalina it crashes and the crash log error reason (NSCFConstantString stringByAppendingString:]: nil argument) is incorrect, as diagnosed by a series of log statements. The statement on which it fails is calling setSelectionIndex on an ImagesController class, which uses the NSArrayController interface.
