When building an app with iOS 26 SDK the metadata generator is partly broken due to some changes in how the UIKit.framework is structured. The macro "UIKIT_EXTERN" that was previously defined in UIKit/UIKitDefines.h has been moved to UIUtilities/UIDefines.h. The UIUtilities is located in a new folder called SubFrameworks located in Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library. The macro is used throughout UIKit and anything that depends on it will result in an error when generating the metadata.

The issue can be solved by adding another path to FRAMEWORK_SEARCH_PATHS: $(SDKDIR)/System/LIbrary/SubFrameworks.