Error: Cannot generate efficient code for retrieving the metaType of a composite type without an element name.

https://code.qt.io/cgit/qt/qtdoc.git/tree/examples/demos/coffee/ApplicationFlow.qml?h=6.8#n33

this gives

    espresso: [ApplicationFlow.qml:38:5]
      result: Error: Cannot generate efficient code for retrieving the metaType of a composite type without an element name.
      duration: 585us 

to avoid this error need to convert "alias" to the "explicitly property type".

and use "id" to access the property, this I can understand because of the unqualified access.

but why cannot use "alias"

and is "alias" the same as "explicitly property type" internally?