It seems the permissions of the
apps/joomla/htdocs folder are not correct. Could you execute the following commands:
sudo chown -R bitnami:daemon /opt/bitnami/apps/joomla/htdocs
sudo chmod -R g+x /opt/bitnami/apps/joomla/htdocs
And restart Apache?
/opt/bitnami/ctlscript.sh restart apache
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