I just left a comment here https://www.drupal.org/project/webform_civicrm/issues/3320379#comment-14997370 and figured this module might be a good place for dealing with CiviCRM submissions without triggering the whole CiviCRM processing.

This looks like a promising hook:

hook_webform_handler_invoke_alter(\Drupal\webform\Plugin\WebformHandlerInterface $handler, $method_name, array &$args)

If the CiviCRM handler is disabled then there would need to be a submission handler specific for the webform_civicrm_submissions table, similar to D7WebformSubmission in the webform_migrate module.