[PyQt] macOS dark mode support problems

[Barry Scott]

I have been building apps on macOS using py2app
and PyQt5. To have dark mode work I add this setting to
the Info.plist:

	<key>NSRequiresAquaSystemAppearance</key>
	<string>false</string>

This worked well with:

macOS 10.15.4
Python 3.7.3 final 0
PyQt 5.12.2, Qt 5.12.3

Now I have updated to use:

macOS 10.15.4
Python 3.8.0 final 0
PyQt 5.14.2, Qt 5.14.2

When the .app starts the window appears but is just a grey
rectangle with none of the widgets visible on it.

If I edit the Info.plist and set NSRequiresAquaSystemAppearance
to true the widgets are drawn, but the title bar is the
light-mode version.

What is required to allow dark-mode to be used with Qt 5.14?

Barry