public List<SelectListItem> zplx { get; set; }

  [BindProperty]

  public Qy_Gw Qy_Gw { get; set; } = new();

 zplx = ManageHelper.DropSelect("pz_gwxz", "dictname", "length(dictno)=4", "dictno asc");

 <select class="form-select" asp-for="Qy_Gw.zplx" asp-items="Model.zplx" lay-verify="required">

     <option value="">请选择</option>

 </select>