In the previous post in this series, I described how we rebuilt our ctools page elements as block plugins.
That gave us the new implementations, but not the pages that had already been assembled in Drupal 7. Recreating them manually would have taken a long time and risked losing existing configuration along the way.
We did not want to migrate complete Panels displays. The rebuilt site had its own Layout Builder sections and layouts. We wanted to preserve the page elements, their order and as much of their configuration as the new block plugins could still use.