Explanation
Permanently delete an end user account
You can permanently delete a deactivated user with the Delete button that appears in the directory screen for that user. You cannot undo this deletion. After the deletion, the user is not visible on the People page and is not returned in API responses. However, any log entries that reference the user are maintained. After deletion you can reuse the user name and other identifiers.
https://support.okta.com/help/s/article/How-do-I-deactivate-and-delete-a-user?language=en_US