您需要将VerticalAlignment="Stretch"添加到您的TabView控件中。下面是您的代码中的一个最小示例。

主窗口.xaml

<Grid RowDefinitions="Auto,*">
    <Button
        Grid.Row="0"
        Click="Button_Click"
        Content="Start" />
    <TabView
        x:Name="TabViewControl"
        VerticalAlignment="Stretch"
        Grid.Row="1" />
</Grid>

主窗口.xaml.cs

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Frame frame = new();
        frame.Navigate(typeof(OrderV));

        TabViewItem tabViewItem = new()
        {
            Header = "Order",
            Content = frame
        };

        tabViewItem.IsSelected = true;
        TabViewControl.TabItems.Add(tabViewItem);
    }
}