generate-crud | automatically generates the physical layer | Generator Utils library

The data model you define is authoritative. Types in the Hydra documentation reflect the ones in PHP classes. Here, the email property is of type object. If you set the related data as a string somewhere, you don't respect this contract anymore. The Hydra documentation is not in sync with the returned data.

You can change the type of the email property in the Hydra documentation by decorating the api_platform.hydra.normalizer.documentation service.

But I would recommend to keep the PHP classes' structure of your entities as close as possible of the structure exposed through the API. Your classes should reflect the output of the API. You can use custom data providers to deal with more complex data structure (ex: ORM entities) before hydrating the structure to expose.