您可以像这样修复此问题
替换

<ContentControl Content="{Binding Content}" />

与

<ContentControl Content="{Binding Header, Converter={StaticResource TabHeaderStringToUcConverter}}" />

因此，TabHeaderStringToUcConverter将根据选项卡标题字符串创建适当的UserControl。
完整示例：

<StackPanel>
    <StackPanel.Resources>
        <converters:TabHeaderStringToUcConverter 
            xmlns:converters="clr-namespace:Namespace.Where.This.Converter.Live"
            x:Key="TabHeaderStringToUcConverter" />
    </StackPanel.Resources>

    <TabControl
        TabStripPlacement="Left"
        ItemsSource="{Binding Menu}">
        <TabControl.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Header}" />
            </DataTemplate>
        </TabControl.ItemTemplate>
         <TabControl.ContentTemplate>
            <DataTemplate>
                <ContentControl Content="{Binding Header, Converter={StaticResource TabHeaderStringToUcConverter}}" />
            </DataTemplate>
        </TabControl.ContentTemplate>
    </TabControl>
</StackPanel>

其中TabHeaderStringToUcConverter为

public class TabHeaderStringToUcConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is string str)
        {
            switch (str)
            {
                case "Campaign":
                    return new RankView();
                // other cases..
            }
        }

        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

最后，在ViewModel中，注解掉Content = new RankView()，并从TabItem类中删除Content属性。