<TelerikTextBox ValueChanged="@( (string s) => MyValueChangeHandler(s) )"></TelerikTextBox>

<TelerikGrid Data=@GridData FilterMode="Telerik.Blazor.GridFilterMode.None" Pageable="true" Height="400px">
    <GridColumns>
        <GridColumn Field=@nameof(Employee.Name) />
        <GridColumn Field=@nameof(Employee.AgeInYears) Title="Age" />
        <GridColumn Field=@nameof(Employee.HireDate) Title="Hire Date" />
        <GridColumn Field=@nameof(Employee.IsOnLeave) Title="On Vacation" />
    </GridColumns>
</TelerikGrid>

@code {
    string searchString { get; set; }

    private void MyValueChangeHandler(string theUserInput)
    {
        GridData = AllData.Where(empl => empl.Name.ToLowerInvariant().Contains(theUserInput.ToLowerInvariant())).ToList();
    }

    private List<Employee> AllData { get; set; }
    public List<Employee> GridData { get; set; }

    protected override void OnInitialized()
    {
        AllData = new List<Employee>();
        var rand = new Random();
        for (int i = 0; i < 100; i++)
        {
            AllData.Add(new Employee()
            {
                EmployeeId = i,
                Name = "Employee " + i.ToString(),
                AgeInYears = rand.Next(10, 80),
                HireDate = DateTime.Now.Date.AddDays(rand.Next(-20, 20)),
                IsOnLeave = i % 3 == 0
            });
        }

        GridData = AllData;
    }

    public class Employee
    {
        public int? EmployeeId { get; set; }
        public string Name { get; set; }
        public int? AgeInYears { get; set; }
        public DateTime HireDate { get; set; }
        public bool IsOnLeave { get; set; }
    }
}