Using RelationChoice in Volto does not work

Development Plone 6 UI (Volto)
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1

I am trying to use a RelationChoice field in Volto, but it does not allow to select an object when editing.

Here is de definition of the field:

widget(
    'relation_choice_field',
     RelatedItemsFieldWidget,
     vocabulary_override=True,
     pattern_options={
         'mode': 'auto',
         'recentlyUsed': True,
         'basePath': '/',
     })
 relation_choice_field = RelationChoice(
     title=("Relation Choice Field"),
     source=CatalogSource(),
     required=True)

In Volto it shows like a selectable with “No options”.