Preset DataGrid Filter

I have a DataGrid with a boolean column. I would like to preset the filter for that column on page load to checked (true) while still allowing the user to cycle through the filter options (checked, unchecked, unspecified). I'm unclear how to set up a preset for the column filter.

Not sure how the grid is bound in your case however you can do something like this:

<RadzenGrid @ref="grid" AllowFiltering="true" FilterCaseSensitivity="FilterCaseSensitivity.CaseInsensitive" AllowPaging="true" PageSize="4"
                AllowSorting="true" Data="@employees" TItem="Employee" ColumnWidth="200px">
        <Columns>
            <RadzenGridColumn TItem="Employee" Property="EmployeeID" Title="Employee ID" />
            <RadzenGridColumn TItem="Employee" Property="Photo" Title="Photo" Sortable="false" Filterable="false">
                <Template Context="data">
                    <RadzenImage Path="@data?.Photo" />
                </Template>
            </RadzenGridColumn>
            <RadzenGridColumn TItem="Employee" Property="LastName" Title="Last Name" FilterValue="@lastName" FilterOperator="eq" />
            <RadzenGridColumn TItem="Employee" Property="FirstName" Title="First Name" />
            <RadzenGridColumn TItem="Employee" Property="Title" Title="Title" />
            <RadzenGridColumn TItem="Employee" Property="TitleOfCourtesy" Title="Title Of Courtesy" />
            <RadzenGridColumn TItem="Employee" Property="BirthDate" Title="Birth Date">
                <Template Context="data">
                    @String.Format("{0:d}", data.BirthDate)
                </Template>
            </RadzenGridColumn>
            <RadzenGridColumn TItem="Employee" Property="HireDate" Title="Hire Date">
                <Template Context="data">
                    @String.Format("{0:d}", data.HireDate)
                </Template>
            </RadzenGridColumn>
            <RadzenGridColumn TItem="Employee" Property="Address" Title="Address" />
            <RadzenGridColumn TItem="Employee" Property="City" Title="City" />
            <RadzenGridColumn TItem="Employee" Property="Region" Title="Region" />
            <RadzenGridColumn TItem="Employee" Property="PostalCode" Title="Postal Code" />
            <RadzenGridColumn TItem="Employee" Property="Country" Title="Country" />
            <RadzenGridColumn TItem="Employee" Property="HomePhone" Title="Home Phone" />
            <RadzenGridColumn TItem="Employee" Property="Extension" Title="Extension" />
            <RadzenGridColumn TItem="Employee" Property="Notes" Title="Notes" />
        </Columns>
    </RadzenGrid>

@code {
    RadzenGrid<Employee> grid;
    string lastName = "Davolio";

    IEnumerable<Employee> employees;

    protected override void OnInitialized()
    {
        employees = dbContext.Employees.ToList();
    }

    protected override Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
           grid.Reload();
        }

        return base.OnAfterRenderAsync(firstRender);
    }
}