$("#msUsers").kendoMultiSelect({
        placeholder: "Select Users...",
        autoClose: false,
        dataTextField: "UserName",
        dataValueField: "UserId",
        virtual: {
            itemHeight: 40,
            mapValueTo: "dataItem",
            valueMapper: function (options) {
                var ids = options.value;
                if (!ids.length) {
                    options.success([]);
                    return;
                }
                $.ajax({
                    url: "/Home/GetUserByIds",
                    traditional: true,
                    data: { ids: ids },
                    success: function (response) {
                        options.success(response.length ? response : []);
                    },
                    error: function (xhr) {
                        console.log("Error:", xhr.responseText);
                    }
                });
            }
        },
        dataSource: {
            transport: {
                read: {
                    url: "/Home/BindUsers",
                    dataType: "json",
                    data: function (options) {
                        return {
                            skip: options.skip,
                            take: options.take,
                            filter: options.filter
                        };
                    }
                },
                parameterMap: function (data, action) {
                    if (action === "read") {
                        return {
                            take: data.take,
                            skip: data.skip,
                            filter: data.filter?.filters?.[0]?.value || ""
                        };
                    }
                    return data;
                }
            },
            schema: {
                data: "Data",
                total: "Total"
            },
            pageSize: 40,
            serverPaging: true,
            serverFiltering: true
        }
    });

function GetUsers() {
    $("#msUsers").kendoMultiSelect({
        placeholder: "Select Users...",
        autoClose: false,
        autoWidth: true,
        /*   tagMode: "none",*/
        dataTextField: "UserName",
        dataValueField: "UserId",
        virtual: {
            itemHeight: 40,
            mapValueTo: "dataItem",
            valueMapper: function(options) {
                var ids = options.value;

                if (!ids.length) {
                    options.success([]);
                    return;
                }

                $.ajax({
                    url: "/Home/GetUserByIds",
                    traditional: true,
                    data: {
                        ids: ids
                    },
                    success: function(response) {

                        if (!response.length) {
                            options.success([]);
                            return;
                        }
                        options.success(response);
                    },
                    error: function(xhr) {
                        console.log("Error:", xhr.responseText);
                    }
                });
            }
        },
        dataSource: {
            transport: {
                read: {
                    url: "/Home/BindUsers",
                    dataType: "json",
                    data: function(options) {
                        return {
                            skip: options.skip,
                            take: options.take,
                            filter: options.filter
                        }
                    }
                },
                parameterMap: function(data, action) {
                    if (action === "read") {
                        return {
                            take: data.take,
                            skip: data.skip,
                            filter: data.filter && data.filter.filters && data.filter.filters[0] ?
                                data.filter.filters[0].value :
                                "" // Default to empty if no filter is applied
                        };
                    } else {
                        return data;
                    }
                }
            },
            schema: {
                data: "Data",
                total: "Total"
            },
            pageSize: 40,
            serverPaging: true,
            serverFiltering: true
        },
        enable: false,
        open: function(e) {

            debugger;
            var multiselect = this;
            var selectedValues = multiselect.dataItems(); // Get the selected value objects

            if (selectedValues.length) {
                var dataSource = multiselect.dataSource;


                var currentData = dataSource.view();


                const selectedUserIds = new Set(selectedValues.map(selected => selected.UserId));


                var remainingUsers = currentData.filter(user =>
                    user.UserId && !selectedUserIds.has(user.UserId)
                );


                var sortedData = selectedValues.concat(remainingUsers);
                console.log(sortedData);


                dataSource.data(sortedData); // THIS BREAKS VIRTUALIZATION!
            }

        },

        height: 400,       
    });
}

function msAssegnatariConoscenza_GetDataSource()
{
 return new kendo.data.DataSource(
  {
   serverFiltering: true,
   schema: {
    data: function (response)
    {
     //...
 return response;}
 },
   transport: {
    read: {
     url: "../Api/Assegnatari_SearchWithUO", //Assegnatari_Search
 contentType: "application/json; charset=utf-8",
 dataType: "json",
 type: "POST"
 },
    parameterMap: function (data, type)
 {
     //...
     return JSON.stringify(data);
 }
   }
  }
 );
}

function msAssegnatariConoscenzaInit(fIsReadOnly)
{
 if (!datiSmistamento.AssConoscenza) datiSmistamento.AssConoscenza = [];

  $("#field_AssConoscenza").kendoMultiSelect({
 autoBind: false,
 dataTextField: "Nome",
 dataValueField: "ID",
 minLength: 3,
 delay: 500,
 height: 300,
 headerTemplate: '...',
 tagTemplate: '...',
 itemTemplate: '...', 
 filtering: function (e)
 {
    if (!e.filter || !e.filter.value)
 e.preventDefault();
 },
   dataSource: msAssegnatariConoscenza_GetDataSource() ,
   value: null,
 select: function (e)
 {
    var dataItem = this.dataItem(e.item.index());
 return selectAssegnatarioConoscenza($(this.element[0]).attr("id"), dataItem, e);
   },
 change: function (e) { return msAssegnatariConoscenza_changeEvent(this, e); }, //Fired when value changed by the user, not form code.
 dataBound: function (e) { e.sender.listView.focusFirst(); return false; }
  });
}

 msAssegnatariConoscenza.value([]);
 msAssegnatariConoscenza.dataSource.data(datiSmistamento.AssConoscenza);
 msAssegnatariConoscenza.value(datiSmistamento.AssConoscenza.map(avmAss => avmAss.ID));

<select id="categories" 
    data-placeholder="Seleziona le categorie"
    data-role="multiselect" 
    data-bind="source: categories, value: detailForm.data.selectedCategories" 
    data-value-field="id"
    data-text-field="name"
    >
</select>

 let kendoMultiSelect = $("#multisel").kendoMultiSelect({
     dataSource: ['item1'],
     value: ['item1'],
     autoClose: false
 }).data("kendoMultiSelect");

$.ajax({
     url: myUrl,
     type: "POST",
     data: window.kendo.stringify({ objId: that.objId }),
     contentType: "application/json",
     cache: false,
     async: true,
     success: function (response) { //response - array (for example: ['new1', 'new2', ...])
         let widget =  $("#multisel").getKendoMultiSelect();
         widget.dataSource = response;
         widget.value = response; //I need all the data to be selected at once
     }
 });