@Lucas_Estefano I am not perfectly sure, what you were already able achieved in v4. However, relationships are not populated by default in v4, but you need to explicitly populate them. With the REST API this can be done by using the GET parameter populate. The wildcard option populate=* populates all available relationships and other relation elements. For more information see https://docs.strapi.io/developer-docs/latest/developer-resources/database-apis-reference/rest/populating-fields.html#population.
I hope this helps?