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

<ConfigProvider>
    <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>
</ConfigProvider>

<AntContainer />

@code{

    RenderFragment Result;

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

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

}