Applies SCIM PatchOp operations to Group metadata. Supported paths are displayName, externalId, and description. Removing description clears it. Changing displayName does not change externalId. The id, schemas, and meta attributes are read-only and cannot be patched. Group membership is unsupported. Unsupported paths, including members, return 400 with scimType invalidPath. The All Users Group Code cannot be changed. Without a projection query the response is 204; with attributes or excludedAttributes it is 200 with the resulting Group representation. Projected Group responses always include id and schemas and never include members.