I wrote up a launch crash that Yardlet, a macOS app, shipped for four days. Built with Xcode 27.1 for a macOS 15 deployment target, it called Logger.isEnabled(type:). The SDK's swiftinterface lists that method under Logger's @available(macOS 11.0, ...) with no availability of its own, but libswiftos.dylib on macOS 15.6.1 doesn't export it, so dyld stopped the app at launch.
The post covers how I found it, the fix (OSLog.isEnabled(type:)), and a short script that compares an executable's strong imports with what the system libraries export on the target Mac.
If anyone knows which macOS version first exports this symbol, I'd like to add it to the post.