One way you can prevent the cell from editing is to handle teh CurrentCellStartEditing event and set e.Cancel = true. I think you will also have to hand CurrentCellCloseDropdown and call CurrentCell.ConfirmChanges to make the selcted date show up in th ecell before you leave teh cell. Here are some snippets.
private void gridDataBoundGrid1_CurrentCellStartEditing(object sender, CancelEventArgs e)
{
GridCurrentCell cc = this.gridDataBoundGrid1.CurrentCell;
if(this.gridDataBoundGrid1[cc.RowIndex, cc.ColIndex].CellType == "MonthCalendar")
e.Cancel = true;
}
private void gridDataBoundGrid1_CurrentCellCloseDropDown(object sender, Syncfusion.Windows.Forms.PopupClosedEventArgs e)
{
if(e.PopupCloseType == Syncfusion.Windows.Forms.PopupCloseType.Done)
this.gridDataBoundGrid1.CurrentCell.ConfirmChanges();
}