Trouble using WhenAnyValue with WhenAnyObservable - wpf

Question

I'm trying to avoid an update to a property if another property is changing. So I've come up with the following (in my ViewModel):
this.WhenAnyObservable(
x => x.WhenAnyValue( y => y.Asset.CurrentValuation ),
x => x.Changing,
(currentValuation, changing) => changing.PropertyName != "CurrentValuationCalculated"
)
However, ReactiveUI throws the following error inside ExpressionRewriter.VisitMethodCall:
throw new NotSupportedException("Index expressions are only supported with constants.")
If I remove the WhenAnyValue line, it works. So I'm assuming it's something to do with the expression inside WhenAnyValue?
Without delving into what the ExpressionRewriter code actually does, what is it complaining about? Have I made some sort of simple error?
Update
So I've entered this instead:
this.WhenAnyObservable(
x => x.Asset.CurrentValuation,
x => x.Changing,
( currentValuation, changing ) => changing.PropertyName != "CurrentValuationCalculated"
)
However, the compiler complains about x.Asset.CurrentValuation and says:
Cannot implicitly convert type 'decimal?' to 'System.IObservable<ReactiveUI.IReactivePropertyChangedEventArgs<ReactiveUI.IReactiveObject>>'

Answer 1

Short answer is yes.
The longer answer is WhenAnyObservable will provide you the change notification, so you don't really need the WhenAnyValue. You would generally use WhenAnyValue on a ViewModel property to force a subscription to the change notification. The observable sequence is inherently providing change notification via OnNext
Edit
Notice below I am observing an IObservable in the WhenAnyObservable and a view model property in WhenAnyValue. You don't need to unwrap the value in the call to WhenAnyObservable to get the value out.
public class MainViewModel : ReactiveObject
{
private string _property;
public IObservable<bool> MyObservabe { get; }
public string MyProperty { get => _property; set => this.RaiseAndSetIfChanged(ref _property, value); }
public MainViewModel()
{
MyObservabe = Observable.Interval(TimeSpan.FromSeconds(1)).Select(x => x > 5);
this.WhenAnyObservable(x => x.MyObservabe);
this.WhenAnyValue(x => x.MyProperty);
}
}