The same codebase previously ran fine when uploaded to TestFlight, but after re-uploading it now fails to launch on iOS 12, even though neither the code nor the Xcode version has changed. I suspect a recent change in the App Store Connect backend processing pipeline is the cause.

Not just Xcode 26 — re-releasing with an older version of Xcode has the same issue. For users on iOS 12 and below, the app can no longer launch.