Some web app may use more specific DB version. For example WITH [recursive] required MariaDB 10.2.1+ ( https://mariadb.com/kb/en/with/ ), or MySQL 8.0+ ( https://dev.mysql.com/doc/refman/8.0/en/with.html )
On my server, there is only MariaDB 10.x.x installed but this plugin returns MySQL version 5.5.5 which is incorrect.
Maybe add more details about DB server info?
WordPress use mysqli, so the server_info ( https://www.php.net/manual/en/mysqli.get-server-info.php ) should work.