ASP.NET Core MVC : can't render fields inside form tag

I'm working on a function that allows agents to check and modify on what inventory their customers bought.

Basically, it's an update form inside a bootstrap modal, which is in a partial view under another partial view.

At first, I tried to bind my view model with the form inside the modal using tag helper. Something like:

<div class="modal-dialog modal-lg">
    <div class="modal-content">
        <div class="modal-header">
            <h5 class="modal-title" id="exampleModalLabel">Update Inventory</h5>
            <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
        </div>
        <form id="UpdateForm" asp-controller="Home" asp-action="UpdateD" data-ajax-method="post" data-ajax="true" data-ajax-success="InsertSuccess"> 
            <div class="modal-body">                           
                <div class="mb-3 row">
                    <label asp-for="FieldExample" class="col-sm-2 col-form-label">FieldExample</label>
                    <div class="col-sm-10">
                        <input asp-for="FieldExample" class="form-control">
                    </div>
                </div>
            </div>
            <div class="modal-footer">                                                   
                <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Close</button>
                <button type="submit" class="btn btn-primary">UpdateBtn</button>
            </div>
        </form>
    </div>
</div>

I checked the form tag was closed properly and the data fields were valid.

But the form turns out to render none of my fields, closing immediately, like this:

<form id="UpdateForm" data-ajax-method="post" data-ajax="true" data-ajax-success="InsertSuccess" action="/Home/UpdateD" method="post"></form>
<div class="modal-body">
 <div class="mb-3 row">
  <label class="col-sm-2 col-form-label" for="PLAN_TYPE">FieldExample</label>
  <div class="col-sm-10">
   <input class="form-control" type="text" id="FieldExample" name="FieldExample" value="test">
  </div>
 </div>
(...other fields)
 <div class="modal-footer">
  <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Close</button>
  <button type="submit" class="btn btn-primary">UpdateBtn</button>
 </div>
 <input name="__RequestVerificationToken" type="hidden" value="...">
</div>

The form doesn't include my data fields for some reason, and I don't know what is making it wrong.

Even if I tried to make a form using a simple form tag with test fields inside, the form is still malformed (with no fields inside).

It will be thankful for me if some suggestions come up (sorry for my language)