FHIR R5 introduces a new field to the ConceptMap resource: https://build.fhir.org/conceptmap-definitions.html#ConceptMap.group.element.target.relationship

This field doesn't exist in R4B, but the ConceptMaps being shipped still include it.

Example:

https://build.fhir.org/branches/R4B/cm-administrative-gender-v2.json.html