Asp.Net MVC _Layout.cshtml Sidebar and Header Model driven part of the Layout

I'm trying to create a _Layout that will be used by all my Views, but my Sidebar and Header will contain data driven by a model. I have tried creating the sidebar and header as PartialViews and call them inside the _Layout.cshtml. That is causing a side effect that, in all my Index views that are used to render a body in Layout I have to pass the same model into them.

Here is how my _Layout looks

<body>
    <section class="body">
       
    <div class="inner-wrapper">
        @{
            Html.RenderPartial("~/Views/Home/_LeftSidebar.cshtml");
        }
        <section class="content-body">
        @{
            Html.RenderPartial("~/Views/Home/_Header.cshtml");
        }
        <div class="row">
        @RenderBody();
        @{
            Html.RenderPartial("~/Views/Home/_RightSidebar.cshtml");
        }
        </div>
        </section>
    </div>
    </section>

And here is how my HomeController looks:

    public async Task<IActionResult> Index()
    {
        return View();
    }
    public PartialViewResult Header()
    {
        return PartialView();
    }
    public async Task<PartialViewResult> LeftSidebar()
    {
        string department = "Departments";
        var departments = await  _unitOfWork.DepartmentRepository.GetAllAsync(department);
        return PartialView(departments);
    }

And this is my _SideBar looks

                 @foreach(var item in Model)
                            {
                             <li class="nav-parent">
                                 <a>
                                     <i class="@item?.Icon" aria-hidden="true"></i>
                                     <span>@item?.Name</span>
                                 </a>
                             </li>
                     }

The Error that I'm getting is

System.NullReferenceException: 'Object reference not set to an instance of an object.' Microsoft.AspNetCore.Mvc.Razor.RazorPage.Model.get returned null.

If I'm not using the PartialViews correct, or I should not use Partial in this case, What should I use?