What should the solutions architect do to deploy the stacks successfully?
Enable the new Regions in all relevant accounts. Specify the CAPABILITY_NAMED_IAM capability during the creation of the stack set.
Use the Service Quotas console to request a quota increase for the number of CloudFormation stacks in each new Region in all relevant accounts. Specify the CAPABILITY_IAM capability during the creation of the stack set.
Specify the CAPABILITY_NAMED_IAM capability and the SELF_MANAGED permissions model during the creation of the stack set.
Specify an administration role ARN and the CAPABILITY_IAM capability during the creation of the stack set.
Explanations:
Enabling the new Regions ensures that CloudFormation can create stacks there. Specifying the CAPABILITY_NAMED_IAM allows the stack to create IAM roles with custom names, which is necessary for the deployment to succeed when using a custom IAM role in the template.
While requesting a quota increase might be necessary for other resources, the issue here is not about quotas. Additionally, specifying CAPABILITY_IAM does not account for the custom name requirement for the IAM role, which requires CAPABILITY_NAMED_IAM.
While specifying CAPABILITY_NAMED_IAM is necessary, the SELF_MANAGED permissions model is not relevant here as the administration role ARN is typically used in an ADMINISTRATIVE role configuration for cross-account operations, not self-managed.
Specifying an administration role ARN is not required unless operating in a cross-account setup. CAPABILITY_IAM alone does not meet the requirement for custom named IAM roles; CAPABILITY_NAMED_IAM is needed.
I infer that the answer is:
Enable the new Regions in all relevant accounts. Specify the CAPABILITY_NAMED_IAM capability during the creation of the stack set.