Is there a way to limit the management of users in Identity Center group to another Identity Center Group?

This approach is not suitable for default identity store directory or, in other words, when your identity store default one from AWS.

Create an iam policy and attach to group A.

The policy should control the action CreateGroupMembership limited to the resources

• Group (B)
• User (*)
• Identity Store (X)

All these resources need defining to allow group A to add any user to group B in identity site x.

https://docs.aws.amazon.com/service-authorization/latest/reference/list_awsidentitystore.html