The Customizations for AWS Control Tower solution combines AWS Control Tower and other highly-available, trusted AWS services to help customers more quickly set up a secure, multi-account AWS environment using AWS best practices.
Thank you for bringing this up @richardkeit. We're not accepting pull requests at this time, but I've gone ahead and made a backlog item with the team to address this discrepancy.
Per this file, python 3.8 is required.
https://github.com/aws-solutions/aws-control-tower-customizations/blob/main/source/src/setup.py#L28