Support

No attachment came but I understand the problem.

It happens because the old mysql extension used by PHP to connect to MySQL and MariaDB database servers was deprecated since PHP 5.5 and completely removed in PHP 7.0 and later. You need to use the mysqli extension to connect to your database server. See the red box in the official MySQL documentation: https://www.php.net/mysql_connect

Also note that this message does not come from our software. We do not have this kind of message anywhere in it and I don't see any similar messages in WordPress either.

For Joomla, you need to edit the configuration.php file and change the $dbtype line as follows:

public $dbtype = 'mysqli';

Please note the trailing i. It makes all the difference. Another option is using pdomysql instead of mysqli, depending on what your server supports. The alternative uses the PDO (PHP Data Objects) extensions which is an ever more modern, faster and more robust way to connect to database servers than the obsolete mysql and the legacy mysqli extensions but it's not as widely supported.

As for WordPress, I am really puzzled because it does not require any special configuration. It automatically detects if your server supports mysqli and uses it instead of the mysql connector. We also do the same in the CLI, JSON API and remote backup endpoints.