@(Html.Kendo().DropDownList()
                    .Name("groupTypeFilter")
                    .HtmlAttributes(new { @class = "form-select", data_alpa = "filter", onchange = "ApplyFilter(this)" })
                    .OptionLabel("All")
                    .DataTextField("Text")
                    .DataValueField("Value")
                    .BindTo(new List<SelectListItem>
                    {
                        new SelectListItem { Text = "All", Value = "all" },
                        new SelectListItem { Text = "All GMS Groups", Value = "allgms" },
                        new SelectListItem { Text = "All MECCOM Groups", Value = "allmeccom" }
                    })  
                    .DataSource(config => config.Read("GetGroupTypes", "Group"))
                    )
 

 
public JsonResult GetGroupTypes()
        {
            var groupTypes = new List<SelectListItem>
            {
                new SelectListItem { Text = "All", Value = "ALL" },
                new SelectListItem { Text = "GMS", Value = "GMS" },
                new SelectListItem { Text = "MEC/COM", Value = "MEC/COM" }
            };
            return Json(groupTypes);
        }
 
It seems to be only load the data from the data call and not the deafult data that I loaded into it 

@model int?

@{
    var initialItems = new List<SelectListItem>()
{
        new SelectListItem{ Text = "Schweiz", Value = "1" }
    };
}

<div class="k-floating-label-container mb-3">
    @(Html.Kendo().DropDownListFor(x => x)
        .DataTextField("Text")
        .DataValueField("Value")
        .AutoBind(false)
        .BindTo(initialItems)
        .Value(Model?.ToString())
        .Events(e => e.Open("onDropDownOpen"))
        .Deferred()
    )
    @Html.LabelFor(x => x, new { @class = "k-label k-input-label" })
    @Html.ValidationMessageFor(x => x)
</div>

<script>function onDropDownOpen(e) {
    var dropdown = $("#Store_DefaultLanguageId").data("kendoDropDownList");

    if (dropdown.dataSource.total() === 1) { 
        dropdown.setDataSource(new kendo.data.DataSource({
            transport: {
                read: {
                    url: "/Language/LanguageList",
                    dataType: "json",
                }
            },
            serverFiltering: true
        }));
    }
}
</script>

                    @(Html.Kendo().DropDownList()
                        .Name("WarehouseId")
                        .OptionLabel("Select a warehouse...")
                        .HtmlAttributes(new { style = "width: 100%" })
                        .DataTextField("Text")
                        .DataValueField("Value")
                        .Value("-1")
                        .DataSource(source =>
                        {
                            source.Read(read =>
                            {
                                read.Action("Inventory_Warehouse_Read", "Purchasing", new { productId = @Model.ProductId});
                            });
                        })
                        .Height(400)
                        )

@(Html.Kendo().Grid<MySeriesModel>().Name("drpSeries")
              .Columns(column =>
              {
                  column.Bound(model => model.SeriesName).HtmlAttributes(new { style = "font-weight: bold" }).Title("No.").Width(40);
                  column.ForeignKey(c => c.SeriesType, (IEnumerable<SelectListItem>)ViewBag.LstSeriesType, "value", "text").HtmlAttributes(new { style = "text-align: left", onChange = "onChangeSeriesType('#=ID#'); setSerieXml();" }).Title("Series Type").MinScreenWidth(60);
                  column.Bound(model => model.SeriesTitle).Title("Series Title").HtmlAttributes(new { onChange = "setSerieXml();" }).MinScreenWidth(120).Encoded(false);
                  column.Bound(model => model.Axis).Title("Axis").ClientTemplate("#=getAxisActionLink(ID,Axis)#").MinScreenWidth(120);                  
                  column.ForeignKey(c => c.Y_Format, (IEnumerable<SelectListItem>)ViewBag.LstSeriesFormat, "value", "text").HtmlAttributes(new { style = "text-align: left", onChange = "onChangeFormat(this);" }).Title("Format").MinScreenWidth(150);
                  column.ForeignKey(c => c.Y_Axis, (IEnumerable<SelectListItem>)ViewBag.ListSerriesYAxis, "value", "text").HtmlAttributes(new { style = "text-align: left", onChange = "onChangeYAxis(this,'#=ID#');" }).Title("Y Axis Scale").Width(100);
                  column.Bound(x => x.ID).ClientTemplate("<button class= 'k-button' type='button' onclick=onRemoveSeries('#=ID#')>" + "Remove" + "</button>").HtmlAttributes(new { style = "text-align: center" }).Title("").Width(120);
              })
              .DataSource(dataSource => dataSource
                    .Ajax()
                    .ServerOperation(false)
                    .Model(model =>
                    {
                        model.Id(item => item.ID);
                        model.Field(item => item.ID).Editable(false);
                        model.Field(item => item.SeriesName).Editable(false);
                        model.Field(item => item.Axis).Editable(false);
                        model.Field(item => item.SeriesTitle).Editable(false);
                    })
                    .Read(read => read.Action("SeriesList_DataSource", "Dashboard").Data("getDataForDgdSeries_Read"))
               )
               .Events(e =>
               {
                   e.DataBound("onDataBoundDgdSeries");
               })
               .Resizable(x => x.Columns(true))
               .AutoBind(true)
               .Scrollable(x => x.Enabled(true))
               .Editable(editable => editable.Mode(GridEditMode.InCell))
               .Selectable(selectable => selectable.Mode(GridSelectionMode.Single))
               .HtmlAttributes(new { style = "overflow: auto; width:100%", @class = "form-group" })

)

function onChangeSeriesType(id) {
    drpSeries = $('#drpSeries').data('kendoGrid');
    dataSource = drpSeries.dataSource;
    var lstSerieRow = dataSource.data();
    if (lstSerieRow[id - 1].Axis.length > 0) {
        lstSerieRow[id - 1].SeriesTitle = "";
        lstSerieRow[id - 1].Axis = "";
        dataSource.fetch();
    }
}

public class MySeriesModel
{
    public string ID { get; set; }

    public string SeriesName { get; set; }
    public string AxisName { get; set; }
    public string Axis { get; set; }
    [AllowHtml]
    [UIHint("GridDropDownList")]
    public string SeriesType { get; set; }

    public string SeriesTitle { get; set; }

    public string X_Ordinate { get; set; }

    public string X_Format { get; set; }

    [AllowHtml]
    [UIHint("GridDropDownList")]
    public string Y_Format { get; set; }

    [AllowHtml]
    [UIHint("GridDropDownList")]
    public string Y_Ordinate { get; set; }
    [AllowHtml]
    [UIHint("GridDropDownList")]
    public string Y_OrdinateTo { get; set; }
    public string TOOLTIP_FORMAT { get; set; }

    [AllowHtml]
    [UIHint("GridDropDownList")]
    public string Y_Axis { get; set; }
}

public ActionResult RenderSeriesConfig(string viewName)
{
    List<SelectListItem> seriesType = GetDashboadChartStyleTypeList();
    string arrSeriesType = "";
    for (int i = 0; i < seriesType.Count; i++)
    {
        arrSeriesType += seriesType[i].Text.ToString() + "," + seriesType[i].Value.ToString() + ";";
    }
    ViewBag.LstSeriesType = seriesType;
    ViewBag.ArrSeriesType = arrSeriesType;
    ViewBag.LstSeriesAxis_Ordinate = GetLstFieldNamesSelectListItem(viewName);
    ViewBag.LstSeriesFormat = GetFormatShortList();
    ViewBag.ListSerriesYAxis = GetYAxisSettingList();
    return PartialView("_ChartDetail_Series");
}