I have the following development environment.
XCode 14.0.1, Qt 5.15.2 and Qt 6.4 both are installed.
Testing on physical Iphone 13 9th Generation device running IOS15.7.

I have an application that is deployed on App store. Due to a bug listed in this Qt bug tracker,
https://bugreports.qt.io/browse/QTBUG-98651
the application started hanging on all new Iphone 12 + devices. Hence based on the suggestions on this link, decided to upgrade Qt to 6.4.

When I tested with a simple application, the bug looks to be resolved with Qt6.4.

Current status on Qt15.5.2 : The application is deployed on the device and works except for the bug. Other than the bug, all things work properly.

Current status on Qt6.4 : After making the necessary changes from Qt5 to Qt6 the application builds however at deployment I get this error,

"Error: You are creating QApplication before calling UIApplicationMain.
If you are writing a native iOS application, and only want to use Qt for
parts of the application, a good place to create QApplication is from within
'applicationDidFinishLaunching'
inside your UIApplication delegate."

I have been trying to find a solution to this but I could not find any that is related to qmake. One solution on this forum for this problem seems to be with Cmake which I do not use for the application.

Any suggestions on what could be wrong in this migration?