Hi !
Do you use php-fpm ?
If you use it, maybe it can help you :
systemctl edit php-fpm.service and add :
[Service]
ReadWritePaths = /mnt/euler/nextcloud/data/
ReadWritePaths = /usr/share/webapps/nextcloud/apps
ReadWritePaths = /etc/webapps/nextcloud/config/
Source : Cannot write into "config" directory after upgrade - #2 by quiwy
Yes, unfortunately. I don’t have another idea but if you need help we are here !!