https://koha-community.org/manual/19.11/en/html/cron_jobs.html?highlight=cron#update-child-to-adult-patron-type The 19.11 manual still references the j2a cronjob, which has been removed as of 19.11 and replaced with update_patrons_category.
I think I might have missed your merge request for this one Ella, did you finish it off?
This is done in 20.11