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/Spreadsheet/Gui/qtcolorpicker.cpp

@@ -46,7 +46,7 @@
 ****************************************************************************/
 
 #include <QApplication>
-#include <QDesktopWidget>
+#include <QScreen>
 #include <QPainter>
 #include <QPushButton>
 #include <QColorDialog>
@@ -315,7 +315,7 @@ void QtColorPicker::buttonPressed(bool toggled)
     if (!toggled)
         return;
 
-    const QRect desktop = QApplication::activeWindow()->geometry();
+    const QRect desktop = QApplication::primaryScreen()->geometry();
 
     // Make sure the popup is inside the desktop.
     QPoint pos = mapToGlobal(rect().bottomLeft());
@@ -872,7 +872,7 @@ void ColorPickerPopup::regenerateGrid()
     // one.
     if (grid) delete grid;
     grid = new QGridLayout(this);
-    grid->setMargin(1);
+    grid->setContentsMargins(1, 1, 1, 1);
     grid->setSpacing(0);
 
     int ccol = 0, crow = 0;