One of our big Drupal 7 to Drupal 9 migration projects included bringing across image cropping functionality and data on a longstanding client's website. This site had used the Imagefield Crop module, but that was only for Drupal 7. We set up Image Widget Crop for the new site, which is better in a few ways but is also fundamentally different. The old site referenced the cropped images from content, only bringing in the originally-uploaded images for edit pages, to allow editors to adjust the cropping, which was then used wherever that image appeared on the frontend. But the new Image Widget Crop module allows configuring different crops for different situations.
The real challenge was in migrating the data! But we call ourselves Drupal experts, so of course we dug to find solutions. We found the following steps were necessary...