If you force transparency of label by overwriting delegate of item view as follow :

bool item::customData(
    const QString& fieldName,
    int role,
    QVariant& data
) {
    if (fieldName == NAME_COLUMN) {
        if( role == Qt::ForegroundRole) {
            QColor c = qApp->palette().brush(QPalette::Text).color() ;
            c.setAlpha(0) ;
            data = QBrush(c);
            return true;
        } else if( role == Qt::BackgroundRole) {
            QColor c = qApp->palette().brush(QPalette::Background).color() ;
            c.setAlpha(0) ;
            data = QBrush(c);
            return true;
...

this change affect the transparency of checkmark.