The error message you’re encountering indicates that the database type in your Moodle config.php file is set to 'mysqli', but it needs to be changed to 'mariadb'. To fix this, follow these steps:

1. Open the config.php file located in your Moodle installation directory.
2. Locate the line that specifies the database type, which will look something like this: $CFG->dbtype = 'mysqli';
3. Change 'mysqli' to 'mariadb', so it looks like this: $CFG->dbtype = 'mariadb';
4. Save the config.php file.
5. Try accessing your Moodle site again to see if the issue is resolved.

This change tells Moodle to use the MariaDB driver instead of MySQL, which should resolve the error if you are using MariaDB as your database.