What is the MOST operationally efficient way to meet this requirement?

Explanations:

Creating a CloudFormation template to use the AWS Service Catalog portfolio does not directly replicate the portfolio or its contents in the new account. Instead, it would require additional steps to configure resources and services, making it less operationally efficient.

Manually creating an AWS Service Catalog portfolio in the new account duplicates the original portfolio but is time-consuming and error-prone, thus not operationally efficient. It requires manual effort and does not leverage existing resources or automation.

Running a Lambda function to create a new AWS Service Catalog portfolio based on the DescribePortfolio API operation is not a straightforward solution. While it automates some aspects, it still requires a deeper understanding of the API and does not ensure a complete and accurate replica of the existing portfolio.

Sharing the AWS Service Catalog portfolio with the new AWS account is the most operationally efficient method. It allows for the direct replication of the portfolio and its associated products without the need for manual recreation or additional configurations, facilitating quick and accurate setup in the new account.