Ok I managed to get it through to App Store Connect! Had to replace the call to macdeployqt with Xcode's equivalents :( Got some helpful info from Apple, details on this thread if anyone's interested https://developer.apple.com/forums/thread/740606

@maximo Did you finally submit an app to the Mac App store and which web incarnation of Qt did you use ?

Hi and welcome to devnet,

The QtWebView module doesn't use QtWebEngine at all. The module naming is a bit confusing but that's all. QtWebView is a thin layer to use the native web view