When ComboBox is drawn and rotated in the following way, it does not appear to be rotated on macOS but it does on Windows.

QPainter painter;
...
 // Create the style option.
 QStyleOptionComboBox option;
 option.initFrom(this);

 painter.rotate(-90);

 style()->drawComplexControl(QStyle::CC_ComboBox, &option, &painter);

How to reproduce
1. Use qtbug98935ーmdi-noteRotate.zip ( Modified version of Qt mdi example )
2. Click New button

On macOS

On Windows