public class BindingToReadOnlyPropertyBehavior : Behavior<DependencyObject>
    {
        public PropertyPath Property { get => binding.Path; set => binding.Path = value; }
 
        private readonly Binding binding = new Binding("") { Mode = BindingMode.OneWay };
 
        protected override void OnAttached()
        {
            binding.Source = AssociatedObject;
            BindingOperations.SetBinding(this, SourceProperty, binding);
        }
 
        /// <summary>Приватное свойство для получения данных 
        /// по заданной привязке</summary>
        private object Source
        {
            get { return (object)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }
 
        // Using a DependencyProperty as the backing store for Source.  This enables animation, styling, binding, etc...
        private static readonly DependencyProperty SourceProperty =
            DependencyProperty.Register("Source", typeof(object), typeof(BindingToReadOnlyPropertyBehavior), new PropertyMetadata(null, propertyChangedCallback));
 
        /// <summary>Метод обратного вызова для передачи полученного значения 
        /// в целевую привязку</summary>
        /// <param name="d"></param>
        /// <param name="e"></param>
        private static void propertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
            => ((BindingToReadOnlyPropertyBehavior)d).Target = e.NewValue;
 
        /// <summary>Целевой объект куда должно передаваться значение</summary>
        public object Target
        {
            get { return (object)GetValue(TargetProperty); }
            set { SetValue(TargetProperty, value); }
        }
 
        // Using a DependencyProperty as the backing store for Target.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty TargetProperty =
            DependencyProperty.Register("Target", typeof(object), typeof(BindingToReadOnlyPropertyBehavior), new PropertyMetadata(null));
 
    }

    public class VMClass : OnPropertyChangedClass
    {
        public double Width { get => _width; set { _width = value; OnPropertyChanged(); } }
        private double _width;
    }

    <Window.DataContext>
        <local:VMClass/>
    </Window.DataContext>
    <Grid>
        <i:Interaction.Behaviors>
            <local:BindingToReadOnlyPropertyBehavior  Target="{Binding Width, Mode=TwoWay}" Property="ActualWidth" />
        </i:Interaction.Behaviors>
        <TextBlock Text="{Binding Width}"/>
    </Grid>