It’s not possible to have a running joomla site without the libraries folder. It’s located at the root of your Joomla installation. I hope this is the location you are looking at.
Also, in the Q/A you linked, there is more than 1 answers. So make sure you read everything there. You could try the second answer as well, to enable Joomla FTP layer.
Additionally make sure all Joomla directories are writable, just in case you have any permissions issues. You can go into your backend System -> System Information -> Folder Permissions and look down the tree of your directories tree if all dirs are writable (green).
Joomla System Information – Directory Permissions
Finally you can ask for advice from your hosting provider, and maybe they could make the appropriate changes on the server/php configuration (maybe with a custom php.ini or in htaccess).
For example you could define your own value for open_basedir directive, to the appropriate location for your site like:
open_basedir = /home/username/public_html:/tmp
open_basedir = /var/www/vhosts/domain/httpdocs/:/tmp/
In addition, if open_basedir is set, it may be needed to set also the PHP upload_tmp_dir directive to a path that’s inside the open_basedir scope.
What will work for you depends on your environment, so your hosting provider should be able to assist you or give you the right information.
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Replace line 174 in plugins/system/t3/includes/joomla30/modulehelper.php
$params = new Registry;
$params = new JRegistry;
Have a look in the index.php file for the tempate. If it says
defined( ‘_VALID_MOS’ ) or die( …
and legacy mode is off, this will cause this error.
Change _VALID_MOS to _JEXEC and you should be ok to continue.
Hope this helps.