https://www.drupal.org/project/provision/issues/2953349
Aegir 3 is incompatible with Drush 9+ [#2953349] | Drupal.org
Feb 20, 2024 - Problem Given that: Aegir 3 assumes a global Drush, which must be Drush 8 or lower. Drush 9 and above operate only as site-local instances. Modern Drupal 8...
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