FHIR R4B introduces the new CodeableReference datatype.

It also includes some ElementDefinition resources that use this new data type like RegulatedAuthorization.indication 

      {
        "id": "RegulatedAuthorization.indication",
        ...
        "type": [
          {
            "code": "CodeableReference",
            "targetProfile": [
              "http://hl7.org/fhir/StructureDefinition/ClinicalUseDefinition"
            ]
          }
        ],
        ...

However, this violates the ElementDefinition eld-17 constraint which has the following expression in R4B:

(code='Reference' or code = 'canonical') or targetProfile.empty()

Note that in the latest draft of R5 at https://build.fhir.org/elementdefinition-definitions.html this ElementDefinition constraint has already been fixed to include CodeableReference.

I think the same change should be applied to FHIR R4B.