For the record my Nextcloud jail is now over a year old and migrated from warden to iocage under FreeNAS 11.1 and are now living happily on FreeNAS 11.2-RC1. You don’t need the plugin, it’s not hard to follow the admin guide and or augmented third party guides.
@danb35 ’s script to install it hands off in a standard jail is also worth looking at.