Currently, you can only toggle custom fields for student and staff profiles either on or off.
If you store both data that you want to be exported as well as sensitive/special category data in custom fields, you cannot allow custom fields through an API as you cannot prevent the sensitive or special category data from being accessed. This creates potential GDPR compliance issues, particularly with data minimisation and Article 9.
It would be fantastic if there was an option to either allow custom fields by group/category, or by individual fields.