Drush installed in local directory but command not found?
You are calling a global command. Which is not installed or symlinked into one of your Mac's autoloaded bin directories (or is not added to your global $PATH).

Simplest option you have now is to use the local command:

$ cd mydrupal
$ vendor/drush/drush/drush status


Alternatively you may want to install Drush Launcher on your Mac (to be used together with the Composer template for Drupal projects). Which when you are inside a project that has a local Drush installed automatically associates the global drush command to the project's local Drush.