Observes both collection changed and items changed.

ObservableCollectionAndItems.cs

internal class ObservableCollectionAndItems<TModel> where TModel : INotifyPropertyChanged
{
    private readonly ObservableCollection<TModel> collection = new();

    public event EventHandler<EventArgs>? ItemChanged;
    public event EventHandler<NotifyCollectionChangedEventArgs>? CollectionChanged;

    public ObservableCollectionAndItems()
    {
        collection.CollectionChanged += Collection_CollectionChanged;
    }

    private void Collection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        CollectionChanged?.Invoke(sender, e);
    }

    private void Item_PropertyChanged(object sender, EventArgs e)
    {
        ItemChanged?.Invoke(sender, e);
    }

    public void Add(TModel model)
    {
        model.PropertyChanged += Item_PropertyChanged;
        collection.Add(model);
    }

    public bool Remove(TModel model)
    {
        model.PropertyChanged -= Item_PropertyChanged;
        return collection.Remove(model);
    }

}