Need to show the down arrow in dropdown list in ASP.NET Core MVC - asp.net-core-mvc

Question

Working on an ASP.NET Core 6 MVC app. I am created a dropdown using the select asp-for tag helper. But I am not seeing a dropdown down arrow. Also I want to set the top or particular value selected by default.
Below is code and image of a dropdown
<div class="col-sm-3">
<select name="products" class="form-control "
asp-items="#(new SelectList(ViewBag.ddaircraft,"id","name"))">
</select>
</div>
Action Method code for ViewBag:
Public IActionResult Index()
{
var countries= _countries.getCountries();
//add an country item on the top of list.
countries.Insert(0, new Aircraft { Registration="0"});
//i used the country.name for value and item
var ddforAircraft = from country in countries
select new { id = country.name, name=country.name=="0"?"Item List":country.name };
// ddforAircraft.Append(new { id = "0", name = "" });
ViewBag.ddaircraft = ddforAircraft;
return View()
}

Answer 1

I found the answer, after Tiny Wang pointed me to the direction which really helped me to search the answer.
In order to see the dropdown down arrow I added a css class "form-select" without removing anything and I started to see the down arrow
<div class="col-sm-3">
<select name="products" class="form-control form-select-sm form-select " asp-items="#(new SelectList(ViewBag.ddaircraft,"id","name"))">
</select>
</div>

Answer 2

Missing dropdown arrow resulted from the class form-control, I test in my side and I found the arrow can be seen by default until I add class="form-control " to my code:
removing this 2 options then the arrow appeared again, so it proved to relate to the class, you may need to update the style:
Then I use Jquery to change the default selected option when page is loading in my code, my selector has Id Country, then change the value(ListItem.Value):
<select asp-for="Country" asp-items="#(new SelectList(Model.Countries, nameof(ListItem.Value), nameof(ListItem.Text)))">
<option>Please select one</option>
</select>
#section Scripts{
<script>
$("#Country").val('Canada')
</script>
}