ant-design-blazor/site/AntDesign.Docs/App.razor

<ConventionRouter AppAssembly="@typeof(MainLayout).Assembly">
    <Found Context="routeData">
        <RouteView RouteData="routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <LayoutView Layout="@typeof(MainLayout)">
            @if (Result != null)
            {
                @Result
            }
        </LayoutView>
    </NotFound>
</ConventionRouter>

<AntContainer />

@code{

    RenderFragment Result;

    protected override async Task OnInitializedAsync()
    {
        await base.OnInitializedAsync();
        await Task.Delay(2000);

        Result = @<Result Status="404"/>;
    }

}