This cron job setup you can use for file retention policy, trashbin cleanup etc.

To check existing cronjob for user www-data:

crontab -u www-data -l

cron11

To edit for add new cronjob:

crontab -u www-data -e

cron2

Add this script at the bottom of line:

*/5 * * * * php -f /var/www/nextcloud/cron.php

cron3

Verify if the cron job has been added and scheduled:

crontab -u www-data -l