Synchronization nextcloud and folder media dokuwiki

Hello,
I still want to synchronize a folder on my server that is located here:
/var/www/dokuwiki/data/media/wiki
with nextcloud for that I found the link:
https://docs.nextcloud.com/server/12/admin_manual/configuration_files/external_storage/local.html
The commands to be set up are therefore these:

sudo -u www-data chown -R www-data:www-data /localdir
sudo -u www-data chmod -R 0750 /localdir

For my part I named my folder under nextcloud like this:
wiki_local
So, under nextcloud, I need to configure this path:
/var/www/dokuwiki/data/media/wiki
In addition I have to type something like this in ssh I imagine

sudo -u www-data chown -R www-data:www-data /wiki_local
sudo -u www-data chmod -R 0750 /wiki_local

This implies that a www-data group exists which is the case because using the command

cat /etc/group | awk -F: '{print $ 1}'

I get this group but typing

cat /etc/passwd | awk -F: '{print $ 1}'

to list users I do not have a user www-data
I think I’m making a mistake somewhere but where?
Could you help me? Thank you.