For some case, create/using IAM Roles is restricted in AWS Academy. You can only use existing IAM Roles and won't beable to create it for all AWS resources. One of example is CDK role for bootstraping environments.
For example when use AWS Academy Lab, you only have one Role called LabRole
for all resources. It is not possible to create IAM Role in AWS Academy Lab because AWS Academy Lab restrict it dan you won't beable to create IAM Role. You can only use pre-defined IAM Roles from AWS Academy Lab.