AFT Control tower New Account

AWS Control Tower only manages accounts in OUs that it creates or that are enrolled with it.

Make sure the OU you're trying to create the account in is managed by Control Tower. You can check this in the Control Tower dashboard, under "Organizational units". If the OU is not listed there, it means it's not managed by Control Tower.

The following can help you how to enroll OU

https://docs.aws.amazon.com/controltower/latest/userguide/how-to-register-existing-ou.html

If you need further information you can follow this workshop

https://catalog.workshops.aws/control-tower/en-US/introduction/manage-ou