This guide explains why the classic Drush and Symfony dispatch fatal error happens, how to fix it with a project-local Drush install, and how to troubleshoot legacy Drupal stacks without making dependency drift worse.
The Drupal Shell is an amazing tool if you maintain Drupal web sites and you have shell access to the server, where the Drupal site is hosted. This is also an unvaluable tool if you develop i in Drupal.
Drush 8
Updating drush: composer global update drush/drush