Nginx needs access to the apps files so you have to change ownership (and maybe permissions). For example, for Nextcloud :
chown -R nextcloud:www-data /var/www/nextcloud
And did you try
yunohost tools regen-conf dovecot
Nginx needs access to the apps files so you have to change ownership (and maybe permissions). For example, for Nextcloud :
chown -R nextcloud:www-data /var/www/nextcloud
And did you try
yunohost tools regen-conf dovecot