Get-MgGroupMember doesn't return service principals as group members

Describe the bug

I was trying to list all members (users, nested groups, devices, service principals) of certain Entra ID groups, using Get-MgGroupMember cmdlet. I found that in a list of groups I was interested in I found only one user, but in fact there was a user and service principal.

I checked another group that has SPs as group members only and Get-MgGroupMember showed that it is empty.

Expected behavior

According to the cmdlet synopsis, Get-MgGroupMember should do following:

Get a list of the group's direct members.
A group can have users, organizational contacts, devices, service principals and other groups as members.

But in fact it doesn't display SPs.

How to reproduce

1. Create an Entra ID group with a service principal member.
2. Execute Get-MgGroupMember -GroupId $GroupId.
3. Observe missing SP id in the output.

SDK Version

2.20.0

Latest version known to work for scenario above?

No response

Known Workarounds

No response

Debug output

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### Configuration

- OS: Windows 11
- OS Build: 22H2 22621.3737
- Arch: x64
- PSVersion: 5.1.22621.3672

### Other information

_No response_

Start with the Get-MgGroupMember cmdlet and reproduce the issue using an Entra ID group containing a service principal, as described in the three-step report. Compare the command output with the group's actual direct members. Done means service principal IDs appear alongside users, nested groups, and devices without omitting them.