When running the attached project QtColors.zip on Windows 11, you can see, that the background of QCheckBox and QRadioButton is transparent (Win11.png):

Background color is blue (like parent widget)
Expected background color would be light grey as seen in Win11Example1.png and Win11Example2.png, independent of the parent widgets background color.

(If transparency is really intended here, ignore this bug report. But it would deviate from other software with these native widgets.)