Someone who has experience with AWS Fleet Manager can clarify this?

I created a role “ec2-ssm” with this permission.

I created an EC2 “amazon-linux” instance by attaching the role.

• If I create the instance with public IP, I see the instance under Fleet Manager.
• If I create the instance without public IP, I do not see the instance under Fleet manager.

Is it expected? This amazon diagram shows that Fleet manager can manage private instance? How is that possible?