@inject IJSRuntime _js

@* Move this script to a proper place in your project, the suppress-error hack is to keep it here in the component for easy copy-paste *@
<script suppress-error="BL9992">
    function getComboHighligtedItem() {
        // gets the currently focused item in this particular combobox
        var selItemElem = document.querySelector(".special-combobox .k-item.k-state-focused");
        if (selItemElem) {
            return selItemElem.innerText;
        }
    }
</script>

Selected value: @selectedValue
<br />

<TelerikComboBox OnBlur="@Test" PopupClass="special-combobox"
                 
                 Data="@myComboData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="@selectedValue" 
                    Placeholder="Select an item..." ClearButton="true" Filterable="true" FilterOperator="@StringFilterOperator.Contains">
</TelerikComboBox>

<input placeholder="other form elements" />

@code {
    async Task Test()
    {
        string currInput = await _js.InvokeAsync<string>("getComboHighligtedItem");
        Console.WriteLine("--------------");
        Console.WriteLine(currInput);
        Console.WriteLine("--------------");
        // note - this relies on the item template of the combo rendering the text, or not being used at all
        // if you use other item templates, you may need to delve deeper in the DOM or otherwise recognize the item
        if (!string.IsNullOrEmpty(currInput))
        {
            // match the filter operation to the filter operator of the combo box - Contains in this sample
            var matchingItem = myComboData.Where(itm => itm.MyTextField.ToLowerInvariant().Contains(currInput.ToLowerInvariant())).FirstOrDefault();
            if (matchingItem != null)
            {
                selectedValue = matchingItem.MyValueField;
            }
        }

    }
   
    // just dummy data follows

    IEnumerable<MyDdlModel> myComboData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });

    int selectedValue { get; set; }

    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }
}