WP-CLI PHP MySQL extension missing
After updating PHP from 7.0 to 7.2 and installing the usual
apt-get install php7.2-mysql php-mysql extensions, as well as reloading the server
service apache2 reload && service mysql reload WP-CLI can still produce an error
Your PHP installation appears to be missing the MySQL extension which is required by WordPress when trying to perform basic tasks, even though existing WordPress installations are working fine and are able to interact with MySQL the server, meaning the PHP mysql extension is set up correctly.
The solution is to reload the terminal instance as well. Even though
wp --info reflects the new PHP version there seem to be some internal things that do not get updated without restarting completely.