Hi @tomvanenckevort 👋🏻
I use the API version of ModelsBuilder (latest - "Umbraco.ModelsBuilder 8.1.6"), and noticed that a TextCount wrapped RTE property is returning data as "object":
In the interface for the composition:

In the class for a content type using that composition:

I see there is a PropertyValueConverter in the package, so I'm not sure why this is the result...