The operations defined on ValueSet have options for OperationOutcomes as part of their results.

There is a terminology-specific CodeSystem defined for terminology-related issues: http://hl7.org/fhir/tools/CodeSystem/tx-issue-type.

Request linking to that information from the operation pages (e.g., https://hl7.org/fhir/R5/valueset-operation-validate-code.html).