The usual problem, has to happen at least once each summer I suppose :) Could the person responsible take a moment and update the relevant records please? It's been days now, thanks!
ERROR ITMS-90744: "Unsupported Xcode or SDK Version. Your app was built with a version of Xcode or SDK that is not yet supported for upload to App Store Connect. For more information about supported versions of Xcode and SDK for Testflight or App Store submissions, view the App Store Connect What's New page (https://developer.apple.com/app-store-connect/whats-new/)."