It’s hard to understand what you’re trying to achieve with your given explanation. However, from what I understand, you have a ContentControl or another UIElement with a Content attribute. You could instead add another ContentControl and split your window into two, so you have two ContentControls for the window.

<Window.DataContext>
    <StaticResource ResourceKey="ViewModelCollection" />
</Window.DataContext>
...
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="500" />
        <RowDefinition Height="100" />
    </Grid.RowDefinitions>

    <ContentControl
        Grid.Column="0"
        Grid.Row="0"
        Content="{Binding MainView.CurrentView}">
    </ContentControl>

    <ContentControl
        Grid.Column="0"
        Grid.Row="1"
        Content="{Binding StatusBar.CurrentView}">
    </ContentControl>
</Grid>

To show two different CurrentViews at once, you’ll need to add another class to your project. For example, you can create a StatusBarViewModel class with a RelayCommand to set the CurrentView of your status bar to the appropriate UserControl.

Furthermore, you can create a ViewModelCollection class that holds the MainViewModel and StatusBarViewModel as properties:

class ViewModelCollection
{
    public ViewModelCollection()
    {
        MainView = new MainViewModel();
        StatusBar = new StatusBarViewModel();
    }

    private MainViewModel _MainView;
    private StatusBarViewModel _StatusBar;

    public MainViewModel MainView
    {
        get { return _MainView; }
        set { _MainView = value; }
    }

    public StatusBarViewModel StatusBar
    {
        get { return _StatusBar; }
        set { _StatusBar = value; }
    }
}

Don’t forget to reference your ViewModelCollection in your App.xaml and set it as the DataContext for your window:

<viewModel:ViewModelCollection x:Key="ViewModelCollection"/>

This approach ensures that you can manage multiple views and view models effectively within your window, with each content area bound to its respective view model.

I assume you want “VM B” to know about the changes that are happening in “VM A”. You have couple of options to accomplish this without much effort, I will elaborate on the simplest one:

1. Use a common state class (a manager class), which contains event that informs about changes
   Example:

   public class AppManager
   {
       public event EventHandler<string> AppNameChanged;
   
       public void ChangeAppName(string newName)
       {
           AppNameChanged?.Invoke(this, newName);
       }
   }
   
   public class ViewModelA
   {
       readonly AppManager _appManager;
       public List<string> AppNamesList { get; set; }
       private string _selectedName;
       public string SelectedName 
       { 
           get =>_selectedName;
           set
           {
               _selectedName = value;
               _appManager.ChangeAppName(value);
           }
       }
   
       public ViewModelA(AppManager appManager)
       {
           AppNamesList = new List<string>();
       }
   }
   
   public class ViewModelB
   {
       readonly AppManager _appManager;
   
       public ViewModelB(AppManager appManager)
       {
           _appManager = appManager;
           _appManager.AppNameChanged += (sender, newName) =>
           {
               Console.WriteLine($"New App Name : {newName}");
           };
       }
   }
   

2. Use Messeging systems (for example from Community MVVM toolkit) to send notification. Example:

   public record AppNameMessage(string Name);
   public class Message : ValueChangedMessage<AppNameMessage>
   {
       public Message(string Name) : base(new AppNameMessage(Name))
       {
       }
   }
   
   
   public class ViewModelA
   {
       public List<string> AppNamesList { get; set; }
       private string _selectedName;
       public string SelectedName
       {
           get => _selectedName;
           set
           {
               _selectedName = value;
               WeakReferenceMessenger.Default.Send<AppNameMessage>(new( new (value)));
           }
       }
   }
   
   public class ViewModelB
   {
   
       public ViewModelB()
       {
           WeakReferenceMessenger.Default.Register<AppNameMessage>(this, (sender, message) =>
           {
               Console.WriteLine($"New App Name : {message.Name}");
           });
   
       }
   }
   

Hope that help you out