The CkEditor 4 to 5 upgrade path no longer requires the presence of CKEditor 4. This is in preparation for Drupal 10, so that sites' CKEditor configuration can be upgraded to CKEditor 5 even after the CKEditor 4 integration module is removed from Drupal core.
Without the CKEditor 4 module's presence, there is no way to check if a given configurable plugin is enabled. Following this change, the CKEditor 5 migration process now migrates all plugin configuration. However, Drupal 9.4.4 and higher now no longer store disabled plugin configuration following #3291744: Ensure Editor config entities using CKEditor 4 only store plugins settings for actually enabled plugins. Therefore, so long as sites update to Drupal 9.4.4 and run update.php prior to updating to Drupal 10, there should be no disruption for site owners.
