Qt6 port:

* QApplication::setFallbackSessionManagementEnabled has been removed
* QString::medRef() has been removed. Use QString::mid() again.
* QTextStream::setCodec has been removed
* Use operator QVariant of the QFont class to make code Qt5 and Qt6 compatible
* Signature of QTreeWidget::mimeData() has changed in Qt6. Remove TreeWidget::mimeData() because it doesn't change the implementation
* QLayout::setMargin() is deprecated in Qt5 and has been removed in Qt6. Use QLayout::setContentsMargins()
* QDateTime::toTime_t() is deprecated in Qt5 and has been removed in Qt6. Use QDateTime::toSecsSinceEpoch()
* QDesktopWidget is deprecated in Qt5 and has been removed in Qt6. Use QScreen

src/Mod/Sketcher/Gui/SoDatumLabel.cpp

@@ -36,7 +36,6 @@
 # include <cfloat>
 # include <algorithm>
 # include <QFontMetrics>
-# include <QGLWidget>
 # include <QPainter>
 # include <QPen>
 # include <Inventor/SoPrimitiveVertex.h>
@@ -113,7 +112,7 @@ void SoDatumLabel::drawImage()
         return;
     }
 
-    QFont font(QString::fromLatin1(name.getValue()), size.getValue());
+    QFont font(QString::fromLatin1(name.getValue(), -1), size.getValue());
     QFontMetrics fm(font);
     QString str = QString::fromUtf8(s[0].getString());