Asp MVC CheckBoxFor help needed in postback validation

Question

Probably I'm missing something in this. I need a checkbox to be checked by the user when he submits a form. If he hasn't check the checkbox I need the ModelState.IsValid to be false and return back. All the examples found give me IsChecked() property that I can't get. Here is my code:

model:

    [Required(ErrorMessage = "È necessario confermare di aver letto l'informativa sulla privacy.")]
    [Display(Name = "Informativa sulla Privacy")]
    public bool Privacy { get; set; }

view:

        <div class="row mb-3">
        <div class="col">
            @Html.CheckBoxFor(m => m.Privacy, new { @class = "form-check form-check-inline" })
            @Html.LabelFor(m => m.Privacy)<i>&ast;</i>
        </div>
    </div>

all the other helpers work as expected in the controller, except for the @CheckBoxFor

I see I can get an extension: (m => m.Privacy.IfTrue()), but don't know how to implement it

Thanks for any help!