For hosted View Layers it is possible to set a View Definition, to define what fields or features are available in the view. I would like to be able to set the View Definition for a Related Table in a hosted View Layer as well.
See:
To control what data users see, the owner of a hosted feature layer view, or an administrator, can define what fields or features are available in the view. You can also limit the hosted feature layer view to a specific area by defining a spatial extent. These definitions are saved with the hosted feature layer view and allow you more control over what content people see.
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