Hi Florent,
Thanks for sharing this! Using that new feature needs introducing the unique business ID in the external systems, too, which is not possible in my case.
Where the custom field of the profile resource is not available is the join definition of the enrichment. Only fields from the OOB profile can be selected when creating a new join for the enrichment of the transactional message.
It has been demonstrated to the support staff, too, we are waiting for their feedback.
Thanks,
Kornél