Separately, I tried to reproduce a different GetOverlappedResult() (not Ex) behaviour based on app manifest as described here: https://learn.microsoft.com/en-us/windows/win32/w8cookbook/application--exec...). I could not. Tried every supportedOS GUID listed, one by one and together, made sure that those are getting picked up with kernel32.GetVersion result, maxversiontested (while that is Win 10 addition and should not be related). At least on up to date Windows 11 it had no effect on the mentioned difference, so I left this part alone.