This is really just a note for anyone trying to solve this issue in the future, as I was working through setting up Nextcloud cron.php via HestiaCP - Cron configuration tab, I assumed I had to STATE the “php” entry, and I was incorrect.
Adding this cron job under the HestiaCP user in question works perfectly.
Code that Nextcloud recommends:
php -f /var/www/nextcloud/cron.php
Code that HestiaCP likes:
-f ~/web/(your domain name)/public_html/cron.php
Enjoy, and thanks to all the great work by these devs!