Comment # 1 on bug 1214915 from Fabian Vogt

> You don't have to worry that you brake something if you enable this option as the user also have to set the environment variable QT_XCB_NATIVE_PAINTING to make it work.

Indeed, but then I wonder why it's not enabled by default upstream. Do you
know?

It looks like this is available in Qt 6 as well (also still experimental), so
if we enable this in Qt 5 it should be done for Qt 6 as well.