How to do a simple XAML (WPF) conditional binding on the Visibility property

Since you want to toggle between Hidden and Visible and true is hidden you can either write custom IValueConverter or use simple Style.Trigger

<Button Content="Enable">
    <Button.Style>
        <Style TargetType="{x:Type Button}">
            <Setter Property="Visibility" Value="Visible"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsEnabled}" Value="True">
                    <Setter Property="Visibility" Value="Hidden"/>
                </DataTrigger>
            </Style.Triggers>                    
        </Style>
    </Button.Style>
</Button>

This is all assuming the DataContext is set accordingly and MyModel.IsEnabled raises INotifyPropertyChanged.PropertyChanged event whenever changed

public class MyModel : INotifyPropertyChanged
{
    private bool _isEnabled;

    public bool IsEnabled
    {
        get { return _isEnabled; }
        set
        {
            _isEnabled = value;
            OnPropertyChanged("IsEnabled");
        }
    }

    #region INotifyPropertyChanged

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion
}