Rendering looks pretty bad if opacity graphics effect is applied and scaled factor is non integer.

Sample:
//set non integer scale factor
qputenv("QT_SCALE_FACTOR", QByteArray("1.5"));

QWidget mainWindget;
QLabel label(&mainWindget);
label.setText("Sample Test");
label.setGraphicsEffect(new QGraphicsOpacityEffect(&label));
mainWindget.show();