Unable to create new group inside Administrative Unit using Graph API

Question

I intend to create a new group inside an Administrative Unit in AAD programmatically. I will run this under the context of a service principal.

I am facing 2 issues:

1. Unable to find AddAsync() on Graph SDK version 4.52.0

await graphClient.Directory.AdministrativeUnits["{administrativeUnit-id}"].Members.Request().AddAsync(newGroupObject);

Error - AddAsync missing error

1. GroupAdministrato role on AU: I assigned GroupAdministrator role to my service principal + Directory.Read.All graph API permission, however, I am still not able to create a new group inside AU and it says insufficient privileges.

Endpoint - https://graph.microsoft.com/v1.0/directory/administrativeUnits/40335129-6bd0-4190-a383-a42e3eae09dc/members/

If I assign AdministrativeUnit.ReadWrite.All permission to service principal, I am able to create the group inside AU.

Why is Group Administrator role not working as intended? Am I missing something?

For issue # 2, If I assign AdministrativeUnit.ReadWrite.All permission to service principal, I am able to create the group inside AU.