How to define boolean key in app.xaml?

How to define a global resource dictionary boolean key, ShowMyMenu, and use it to show or hide myMenu

<local:myMenu x:Name="myMenu" HorizontalOptions="FillAndExpand" VerticalOptions="Start" IsVisible="{StaticResource ShowMyMenu}" />

I tried same different ways in App.xaml file, but they can't be executed:

<x:bool x:key="ShowMyMenu">True</x:bool>

<x:Boolean x:key="ShowMyMenu">True</x:Boolean>

<Boolean x:key="ShowMyMenu">True</Boolean>

Thanks for your help