Как обновить ObservableCollection после события Loaded

private ObservableCollection<Client> _clients;
 
public ObservableCollection<Client> Clients
{
    get => _clients;
    set
    {
         _clients = value;
         RaisePropertyChanged(nameof(Clients));
    }
}

public IList<IListMember> ItemsSource
{
    get => (List<IListMember>)GetValue(ItemsSourceProperty);
    set => SetValue(ItemsSourceProperty, value);
}
 
public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.Register(nameof(ItemsSource),
    typeof(IList<IListMember>), typeof(ListUserControl), new FrameworkPropertyMetadata(new List<IListMember>()));

    public interface IHeaderSortDescription
    {
        object Header { get; }
 
        SortDescription Description { get; }
    }

    public class ClientSortDescription : IHeaderSortDescription
    {
        public object Header { get; set; }
        public SortDescription Description { get; set; }
 
        public static ReadOnlyCollection<ClientSortDescription> Descriptions { get; }
            = new ReadOnlyCollection<ClientSortDescription>(new ClientSortDescription[]
            {
                new ClientSortDescription() { Header = "Id по возрастанию", Description = new SortDescription("Id", ListSortDirection.Ascending)},
                new ClientSortDescription() { Header = "Id по убыванию", Description = new SortDescription("Id", ListSortDirection.Descending)},
                new ClientSortDescription() { Header = "Имя по возрастанию", Description = new SortDescription("Name", ListSortDirection.Ascending)},
                new ClientSortDescription() { Header = "Имя по убыванию", Description = new SortDescription("Name", ListSortDirection.Descending)},
            });
 
        public static Func<object, string, bool> FilterForClient { get; } = (s, text) =>
        {
            return s is Client client &&
                    client.Name.Contains(text);
        };
    }