I would like to use Drush 11 but when I try to use commands with drush 11 I see the error:
drush11: command not found
Resolution
Drush 11 is not currently pre-installed on Cloud Platform, however Acquia recommends you require a site-local Drush as part of your codebase, not your home directory, and run your commands with a specific major version of Drush.
To upgrade to Drush 11, you can add it as a project dependency (using Composer) to your Drupal codebase. Drush should be locating in the vendor directory and there should be a drush symlink in the vendor/bin directory.
Using Drush 11 in Cloud hooks
Use the vendor drush from your hooks, instead of using just drush.
Cloud Platform