On https://marmelab.com/react-admin/Fields.html#writing-your-own-field-component, it is recommended to use defaultProps for having a default label for a custom field.

As defaultProps for function components do not exist anymore, another way should be recommended.

Other information:
Mention on defaultProps being removed: https://react.dev/blog/2024/04/25/react-19-upgrade-guide#removed-deprecated-react-apis