Link
Recipe to migrate Drupal 7 Organic Groups to Drupal 9 Group
Despite there are some guides about migrating from OG to Group, as the well written https://thinktandem.io/blog/2018/03/30/migrating-drupal-7-organic-groups-to-drupal-8-group/ , and other guidelines such as https://www.drupal.org/project/group/issues/2826544 companion of https://gitlab.com/geeks4change/hubs4change/h4c/-/tree/608842e73cc02c45deede42556693a9db2a7fc37/modules_dev/h4c_migrate/config/install or https://www.drupal.org/node/2797845 . It's really adapted to your environment how you gonna carry on.