I have the same trouble.
When I use DebounceDelay like 1 second and when my users Press key ENTER after typing text they have wrong value like on this example :

@* SearchInput.razor *@
<form @onsubmit="HandleFormSubmit" @onsubmit:preventDefault>
    <TelerikTextBox Value="@_value"
                    ValueChanged="@HandleValueChanged"
                    Placeholder="Search..."
                    DebounceDelay="@DebounceDelay" />
    <button type="submit">Search</button>
</form>
<p><strong>@_submittedValue</strong></p>
<p>Current internal value: <strong>@_value</strong></p>
@code {
    private int DebounceDelay { get; set; } = 5000; // 5 seconds
    private string _value = string.Empty;
    private string _submittedValue = string.Empty;
    private void HandleValueChanged(string value)
    {
        _value = value;
    }
    private async Task HandleFormSubmit()
    {
        try {
            DebounceDelay = 0;
            var time = DateTime.UtcNow.ToString("mm:ss");
           _submittedValue = $"Submitted value:{_value} at time: {time}";
        }
        finally
        {
            DebounceDelay = 5000; //set back 5 seconds
        }
       await Task.CompletedTask;
    }
}

Can you please fix issue:  ValueChanged not fired before form submit when DebounceDelay is set more than 150 ms.

The title of the request '... OnChange event receive the immediate value ...' is a bit ambiguous. What we need is the OnChange event to fire after the DebouceDelay has passed, like in the construct below. And this should also apply to OnBlur. OnBlur doesn't pass the value to the event handler, but the bound variable should already be updated when OnBlur fires. Otherwise, we have to delay code execution for the binding logic to catch up. The DebounceDelay is a good thing, but events need to be synched with it.

if (DebounceDelay == 0)
{ ... }
else
{
    _debouncer.Debounce(() =>
        { return this.InvokeAsync(() => { ... }); }
, DebounceDelay);
}