You can see that I don’t understand what is the issue, and which permission I need to change on which folder so I don’t receive those Cron error anymore.
I didn’t uninstall anything, I though Nextcloud was an external service, and I don’t use any external service the installation is the default installation.
The Nextcloud data directory is in the MiaB folder ../owncloud/. The folder should be owned by www-data:www-data with 770 permissions and subfolders have 755. Everything in the folder is owned by www-data:www-data, config.php is 600, nextcloud.log is 640 and it looks like the rest of the files are 644.
You have to know that every file or every directory in all of the subdirectories requires the same permissions. When using directories or files that have spaces in the name, you may get errors and either change the permissions for each one or add \n before chmod: