The API documentation included a "state" parameter, but the Read Group API GET/policy/api/v1/infra/domains/{domain-id}/groups/{group-id} was not returning it.
https://developer.broadcom.com/xapis/nsx-t-data-center-rest-api/4.2.2/method_ReadGroupForDomain.html
VMware NSX-T 4.x
The Read Group API GET /policy/api/v1/infra/domains/{domain-id}/groups/{group-id} is an intent API and is not designed to return the realization state of any resource.
From NSX-T 9.1 release, the "state" parameter of the Get Group API is deprecated.
Workaround:
Users will need to use the realized-state status API to check the consolidated status for the NSX-T objects: https://developer.broadcom.com/xapis/nsx-t-data-center-rest-api/4.2.2/method_ReadIntentStatus.html