working with a client that needs to migrate from 2013 to 2019. As a result, and following Nintex migration best practice, we’re looking for detail requirements involved in what are the actions that need to be taken when using detach/attach migration approach from 2013 to 2016; prior to detaching the DB from the 2016 environment to be attached to a 2019 farm. 

1. is the requirement to go through 2016 just a matter of attaching the database from 2013 and then detaching it to be attached to a 2019 instance or there are other actions that MUST be completed within the 2016 instance prior to detaching the database.