Converts the state whether the source object is a collection and it has any item to boolean.

CollectionToBooleanConverter.cs

using System;
using System.Collections;
using System.Globalization;
using System.Windows.Data;

public class CollectionToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is IEnumerable collection)
        {
            foreach (var _ in collection)
            {
                return true;
            }
        }
        return false;
    }

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

This converter should work but in practice, there is almost no use because it will be called only when the source collection is set or replaced.