Currently, the App migration platform was release in an alpha stage. The alpha platform is a set of stable APIs provided to Marketplace partners so they can implement their migration path for CCMA and JCMA. Release posts:

• https://community.developer.atlassian.com/t/build-your-server-data-center-to-cloud-migration-path-with-the-app-migration-platform/40804
• https://community.developer.atlassian.com/t/build-your-server-data-center-to-cloud-migration-path-with-the-app-migration-platform-continued/41204
• https://community.developer.atlassian.com/t/build-your-server-data-center-to-cloud-migration-path-with-the-app-migration-platform-final-steps-release/41391

While Marketplace partners use these APIs, the App migration platform team is working on finishing it by addressing its production readiness.

The current alpha platform has a security issue that makes it not suitable for production migrations involving real customer data.