.....
-->>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>

 <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);
        }

@* Use the Template to render the list of columns and add some custom styles *@ 

<TelerikGrid Data="@MyData"
             Pageable="true"
             PageSize="5"
             Width="700px"
             FilterMode="@GridFilterMode.FilterMenu"
             Sortable="true"
             ShowColumnMenu="true">
     <GridSettings>
     
     <GridColumnMenuSettings Sortable="true"
                             Lockable="false"
                             FilterMode="@ColumnMenuFilterMode.None" />
 </GridSettings>
    <GridColumns> 

 <GridCheckboxColumn Width="80px" HeaderClass="header-select-all" />   
        <GridColumn Field="@(nameof(SampleData.Id))" Width="80px" Title="Id" Id="id-column-id" />
        <GridColumn Field="@(nameof(SampleData.FirstName))" Title="First Name" Id="firstname-column-id" />
        <GridColumn Field="@(nameof(SampleData.LastName))" Title="Last Name" Id="lastname-column-id" />
        <GridColumn Field="@(nameof(SampleData.CompanyName))" Title="Company" Id="companyname-column-id" />
        <GridColumn Field="@(nameof(SampleData.Team))" Title="Team" Id="team-column-id" />
        <GridColumn Field="@(nameof(SampleData.HireDate))" Title="Hire Date" Id="hiredate-column-id" />
    </GridColumns>
</TelerikGrid>

@code {
    public string TextboxValue { get; set; } = string.Empty;

    public IEnumerable<SampleData> MyData = Enumerable.Range(1, 30).Select(x => new SampleData
    {
        Id = x,
        FirstName = $"FirstName {x}",
        LastName = $"LastName {x}",
        CompanyName = $"Company {x}",
        Team = "team " + x % 5,
        HireDate = DateTime.Now.AddDays(-x).Date
    });

    public class SampleData
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string CompanyName { get; set; }
        public string Team { get; set; }
        public DateTime HireDate { get; set; }
    }
}

    <TelerikGrid Data="@myData" Pageable="true" Sortable="true" FilterMode="@GridFilterMode.FilterRow" Groupable="true">
        <GridColumns>
            <GridColumn Field="@nameof(SampleComplexObject.ID)" Title="ID"></GridColumn>
            <GridColumn Field="@nameof(SampleComplexObject.Name)" Title="The Name"></GridColumn>
            <GridColumn Title="First Nested Property" Field="SomeNavigationProperty.Field1">
                <GroupFooterTemplate>
                   Count: @context.Count
                </GroupFooterTemplate>
            </GridColumn>
            <GridColumn Field="SomeNavigationProperty.OtherField" />
        </GridColumns>
        <GridAggregates>
            <GridAggregate Field="SomeNavigationProperty.Field1" Aggregate="@GridAggregateType.Count" />
        </GridAggregates>
    </TelerikGrid>


@code {
    public class SampleComplexObject
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public NestedObject SomeNavigationProperty { get; set; } // use this field name for data binding
    }

    public class NestedObject
    {
        public string Field1 { get; set; }
        public string OtherField { get; set; }
    }

    public IEnumerable<SampleComplexObject> myData = Enumerable.Range(1, 50).Select(x =>
            new SampleComplexObject
            {
                ID = x,
                Name = "Name " + x,
                SomeNavigationProperty = new NestedObject
                {
                    Field1 = "first " + x % 4,
                    OtherField = "second " + x % 6
                }
            }
        );
}

<TelerikGrid Data=@GridData Pageable="true" Height="300px">
    <GridColumns>
        <GridColumn Field="@(nameof(Employee.EmployeeId))">
            <FooterTemplate>
                some footer
            </FooterTemplate>
        </GridColumn>
        <GridColumn Field=@nameof(Employee.Salary) Title="Salary">
        </GridColumn>
        <GridColumn Field=@nameof(Employee.Name)>
        </GridColumn>
    </GridColumns>
</TelerikGrid>

@code {
    public List<Employee> GridData { get; set; } // = new List<Employee>(); // workaround

    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public decimal Salary { get; set; }
    }
}