Your requirements could not be resolved to an installable set of packages.
Problem 1
- acquia/drupal-spec-tool dev-support/5 requires drupal/core ^9.0 -> found drupal/core[9.0.0-alpha1, ..., 9.5.x-dev] but it conflicts with your root composer.json require (11.x-dev).
- acquia/drupal-spec-tool 5.x-dev is an alias of acquia/drupal-spec-tool dev-support/5 and thus requires it to be installed too.
- Root composer.json requires acquia/drupal-spec-tool 5.x-dev -> satisfiable by acquia/drupal-spec-tool[5.x-dev (alias of dev-support/5)].