Fix for XamDataGrid Issue GetAncestor just walks the visual tree looking for Parent of the given type.

KeyDownHandler.cs

public void KeyDownHandler(object sender, KeyEventArgs e)
{
    var cb = (ComboBox)sender;
    if (e.Key != Key.Tab || !cb.IsDropDownOpen)
        return;

    var item = (ComboBoxItem)FocusManager.GetFocusedElement(FocusManager.GetFocusScope(cb));
    cb.SelectedItem = item.Content;
    cb.IsDropDownOpen = false;
                        
    cb.GetAncestor<XamDataGrid>().ExecuteCommand(DataPresenterCommands.CellNextByTab);

    e.Handled = true;
}

XamComboStyle.xaml

<Style TargetType="{x:Type igEditors:XamComboEditor}" x:Key="GridComboFix">
  <Setter Property="ComboBoxStyle">
      <Setter.Value>
          <Style TargetType="ComboBox">
              <EventSetter Event="KeyDown" Handler="KeyDownHandler"></EventSetter>
          </Style>
      </Setter.Value>
  </Setter>
</Style>