public partial class Cat : IRealmObject
{
    [PrimaryKey]
    public ObjectId Id { get; set; } = ObjectId.GenerateNewId();
    public string Name { get; set; } = string.Empty;
    public int Age { get; set; } = 0;
    public string Breed { get; set; } = string.Empty;
}

 public partial class MainWindowViewModel : ObservableObject
 {
     public MainWindowViewModel()
     {
         var config = new RealmConfiguration(@"d:\temp\cats.realm");
         _localRealm = Realm.GetInstance(config);
         CatsQuery = _localRealm.All<Cat>();
     }

     private Realm _localRealm;

     [ObservableProperty] 
     private IQueryable<Cat> _catsQuery;
     
     public Cat? SelectedCat { get; set; }

     [RelayCommand]
     private void RemoveCat()
     {
         if (SelectedCat == null)
             return;
         _localRealm.Write(() => { _localRealm.Remove(SelectedCat); });
     }

     [RelayCommand]
     public void Populate()
     {
         Cat ninja = new() { Name = "Ninja", Age = 1, Breed = "Angora" };
         Cat nounou = new() { Name = "Nounou", Age = 2, Breed = "Siamese" };

         _localRealm.Write(() => _localRealm.Add(nounou));
         _localRealm.Write(() => _localRealm.Add(ninja));
     }
 }

<Window
    x:Class="RealmWinUI.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Content="Populate" Command="{x:Bind MainViewModel.PopulateCommand}" />
        <Button Content="Delete" Command="{x:Bind MainViewModel.RemoveCatCommand}" />

        <ListBox ItemsSource="{x:Bind  MainViewModel.CatsQuery}"
                 DisplayMemberPath="Name"
                 SelectedItem="{x:Bind MainViewModel.SelectedCat, Mode=TwoWay}"/>
    </StackPanel>
</Window>