.....
-->>Clicking on Button for changing grid mode and visibility of columns**
<TelerikToggleButton Title="Oznaceni vice radku" Icon="@FontIcon.ListUnordered" OnClick="@( _  =>{ CurrentStackItem.gSelectionMode=(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple)?GridSelectionMode.Single:GridSelectionMode.Multiple;CurrentStackItem.gSelectedItems = Enumerable.Empty<ExpandoObject>();})"
				Selected="@(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple)"></TelerikToggleButton>
....
<GridColumns>
-->>First "static" 2 columns**
<GridCheckboxColumn Visible=@(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple) @key="@("sIDX")" Width="70px" Locked="true" SelectAll="true" SelectAllMode="GridSelectAllMode.Current"></GridCheckboxColumn><GridColumn FieldType=@typeof(bool) Visible=@(IsPicker==true || (XSmall==false && CurrentStackItem.gSelectionMode==GridSelectionMode.Single )) @key="@("sCMD")" Filterable="false" Sortable="false" Locked="true" Width="@((IsPicker==true && XSmall==true)?"45px":"120px")">
			<HeaderTemplate>&nbsp;</HeaderTemplate><Template Context="ctx"><div @onclick:preventDefault="true" @onclick:stopPropagation="true">

-->> THIS part is hitting LOT OF TIME in debug (expected is at best only once)
				@{if (XSmall==false)
					{
-->> here is LOT OF dynamic buttons.

				}
					</div></Template></GridColumn>

-->> rest of the dynamic columns. In video, starting with "ciiislo org" in header

			@if (GridDef.ColStore != null && GridDef.ColStore.Any())
			{
				foreach (var it in GridDef.ColStore.Where(x => x.Verejny == true))
				{
					<GridColumn @key=@it.FldName Field=@it.FldName FieldType=@it.FldType Title=@it.VerejnyNazev ShowFilterCellButtons="false" Width=@it.cSirkaSestava
					TextAlign=@it.cZarovnani 
					><FooterTemplate>
							@if (it.Sumovat == true)
							{
								@context.Sum
							}
						</FooterTemplate></GridColumn>
				}
			}
		</GridColumns>

@{
    if (GridColumns.Count() > 0)
    {
        <TelerikGrid Data="@Data">
            <GridColumns>
                @foreach (var column in GridColumns)
                    {
                    <GridColumn Field="@column.DataField"
                                ShowColumnMenu="false" Title="@column.DisplayName" Resizable="true" Width="500px">
                        <FooterTemplate>
                            foo
                        </FooterTemplate>
                    </GridColumn>
                    }
            </GridColumns>
        </TelerikGrid>
    }
}

 <TelerikGrid OnRead="ReadItems" EditMode="GridEditMode.Incell"
                     @ref="@GridRef">
    <GridColumns>
      <GridEditDropDownColumn Field="Test1" Data="@Eval?.ListEvaluationTypes" Title="Title" Width="130px" OnChange="OnChangeModel" />
    </GridColumns>
</TelerikGrid>

   private TelerikGrid<EvaluationListDTO> GridRef { get; set; }

   protected async Task OnChangeModel(object model)
        {
            var item = (EvaluationListDTO)model;

            var state = GridRef?.GetState();

           //Save in the Database  

                // use the state to remove the edited item (close the editor)
                state.EditItem = null;
                state.OriginalEditItem = null;
                await GridRef.SetStateAsync(state);
        }

<TelerikGrid @ref="@GridInlineRef"
             Data="@GridInlineData"
             EditMode="@GridEditMode.Inline"
             OnAdd="@OnGridAddEdit"
             OnEdit="@OnGridAddEdit"
             OnCreate="@OnGridInlineCreate"
             OnUpdate="@OnGridInlineUpdate"
             OnRowClick="@OnGridRowClick">
    <GridToolBarTemplate>
        <GridCommandButton Command="Add">Add</GridCommandButton>
    </GridToolBarTemplate>
    <GridColumns>
        <GridColumn Field="@nameof(Product.Name)">
            <EditorTemplate>
                @{ var editItem = (Product)context; }
                <TelerikTextBox @ref="@NameTextBoxRef" @bind-Value="@editItem.Name" DebounceDelay="0" />
            </EditorTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Product.Price)">
            <EditorTemplate>
                @{ var editItem = (Product)context; }
                <TelerikNumericTextBox @ref="@PriceNumericTextBoxRef" @bind-Value="@editItem.Price" DebounceDelay="0" />
            </EditorTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Product.Stock)">
            <EditorTemplate>
                @{ var editItem = (Product)context; }
                <TelerikNumericTextBox @ref="@StockNumericTextBoxRef" @bind-Value="@editItem.Stock" DebounceDelay="0" />
            </EditorTemplate>
        </GridColumn>
        <GridCommandColumn>
            <GridCommandButton Command="Edit">Edit</GridCommandButton>
            <GridCommandButton Command="Save" ShowInEdit="true">Update</GridCommandButton>
            <GridCommandButton Command="Cancel" ShowInEdit="true">Cancel</GridCommandButton>
        </GridCommandColumn>
    </GridColumns>
</TelerikGrid>

@code {
    private TelerikGrid<Product>? GridInlineRef { get; set; }
    private TelerikTextBox? NameTextBoxRef { get; set; }
    private TelerikNumericTextBox<decimal?>? PriceNumericTextBoxRef { get; set; }
    private TelerikNumericTextBox<int>? StockNumericTextBoxRef { get; set; }
    private string EditFieldToFocus { get; set; } = string.Empty;

    private List<Product> GridInlineData { get; set; } = new List<Product>();

    private void OnGridAddEdit(GridCommandEventArgs args)
    {
        EditFieldToFocus = nameof(Product.Stock);
    }

    private async Task OnGridRowClick(GridRowClickEventArgs args)
    {
        EditFieldToFocus = args.Field;
        var itemToEdit = (Product)args.Item;

        args.ShouldRender = true;

        if (GridInlineRef != null)
        {
            var gridState = GridInlineRef.GetState();

            gridState.InsertedItem = null!;
            gridState.OriginalEditItem = itemToEdit;
            gridState.EditItem = itemToEdit.Clone();

            await GridInlineRef.SetStateAsync(gridState);
        }
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (!string.IsNullOrEmpty(EditFieldToFocus))
        {
            await Task.Delay(200);

            switch (EditFieldToFocus)
            {
                case nameof(Product.Name):
                    if (NameTextBoxRef != null)
                    {
                        await NameTextBoxRef.FocusAsync();
                    }
                    break;
                case nameof(Product.Price):
                    if (PriceNumericTextBoxRef != null)
                    {
                        await PriceNumericTextBoxRef.FocusAsync();
                    }
                    break;
                case nameof(Product.Stock):
                    if (StockNumericTextBoxRef != null)
                    {
                        await StockNumericTextBoxRef.FocusAsync();
                    }
                    break;
                default:
                    break;
            }

            EditFieldToFocus = string.Empty;
        }
    }

    #region Programmatic Inline Editing

    private async Task InlineAdd()
    {
        var gridState = GridInlineRef!.GetState();

        gridState.InsertedItem = new Product();
        gridState.InsertedItem.Name = "New value";
        gridState.OriginalEditItem = null!;
        gridState.EditItem = null!;

        await GridInlineRef.SetStateAsync(gridState);
    }

    private async Task InlineEdit()
    {
        if (GridInlineData.Any())
        {
            var gridState = GridInlineRef!.GetState();

            gridState.InsertedItem = null!;
            gridState.OriginalEditItem = GridInlineData.First();
            gridState.EditItem = GridInlineData.First().Clone();
            gridState.EditItem.Name = "Updated inline value";

            EditFieldToFocus = nameof(Product.Price);

            await GridInlineRef.SetStateAsync(gridState);
        }
    }

    private async Task InlineCancel()
    {
        var gridState = GridInlineRef!.GetState();

        gridState.InsertedItem = null!;
        gridState.OriginalEditItem = null!;
        gridState.EditItem = null!;

        await GridInlineRef.SetStateAsync(gridState);
    }

    private async Task InlineUpdate()
    {
        var gridState = GridInlineRef!.GetState();

        if (gridState.EditItem != null)
        {
            OnGridInlineUpdate(new GridCommandEventArgs()
            {
                Item = gridState.EditItem
            });
        }
        else if (gridState.InsertedItem != null)
        {
            OnGridInlineCreate(new GridCommandEventArgs()
            {
                Item = gridState.InsertedItem
            });
        }

        gridState.InsertedItem = null!;
        gridState.OriginalEditItem = null!;
        gridState.EditItem = null!;

        await GridInlineRef.SetStateAsync(gridState);
    }

    #endregion Programmatic Inline Editing

    #region Grid Inline Editing Handlers

    private void OnGridInlineUpdate(GridCommandEventArgs args)
    {
        var updatedItem = (Product)args.Item;
        var index = GridInlineData.FindIndex(i => i.Id == updatedItem.Id);
        if (index != -1)
        {
            GridInlineData[index] = updatedItem;
        }
    }

    private void OnGridInlineCreate(GridCommandEventArgs args)
    {
        var createdItem = (Product)args.Item;
        createdItem.Id = Guid.NewGuid();
        GridInlineData.Insert(0, createdItem);
    }

    #endregion Grid Inline Editing Handlers

    #region Data Generation and Model

    protected override void OnInitialized()
    {
        for (int i = 1; i <= 3; i++)
        {
            GridInlineData.Add(new Product()
            {
                Id = Guid.NewGuid(),
                Name = $"Product {i}",
                Price = Random.Shared.Next(1, 100) * 1.23m,
                Stock = (short)Random.Shared.Next(0, 1000)
            });
        }
    }

    public class Product
    {
        public Guid Id { get; set; }
        public string Name { get; set; } = string.Empty;
        public decimal? Price { get; set; }
        public int Stock { get; set; }
        public DateTime ReleaseDate { get; set; }
        public bool InProduction { get; set; }

        public Product Clone()
        {
            return new Product()
            {
                Id = Id,
                Name = Name,
                Price = Price,
                Stock = Stock,
                ReleaseDate = ReleaseDate,
                InProduction = InProduction
            };
        }
    }

    #endregion Data Generation and Model
}