For PHP version reason, I move Joomla! & CiviCRM from example.org/civicrm to civicrm.example.org. I changed all civicrm.settings.php in admin and frontend folders and I emptied the cache, template_c and log folder and CIVICRM_SITE_KEY is always the same. Everything works fine and cron URL could be fetch (blank screen on the web but Status: 200 after crontab run) So, no mailing is sent automatically. But I can send it when I run the task manually ?!
On CiviCRM status, I can read that no cron is running. But at tihs time, I really don't know where to find to resolve this issue.
I tried both https://example.org/administrator/components/com_civicrm/civicrm/bin/cron.php?name=&pass=&key= and the command wget -O - -q -t 1 'https://example.org/administrator/components/com_civicrm/civicrm/bin/cron.php?name=&pass=&key=', results are OK but CiviCRM doesn't recognize those execution.
I also tried to change PHP version (7.4, 8.0 and 8.1), without any change. I only have a warning about session when I display PHP errors.
On this thread For some reason, cron doesn't work. On CMS joomla, I note that the cron user must be a super-admin, but I tested and it only work once : now, there is an error status with cron in CiviCRM.