How to pull a record from Salesforce and immediately push the node ID back to Salesforce
Here's how I did it...

Since content is set to push (immediately) on update, I added a hook_entity_insert() that responded not to the content insert but the "salesforce_mapped_object" entity.

This ensures that not only was the node/user created but a mapping was created.

/**
 * Implements hook_entity_insert().
 */
function MYMODULE_entity_insert(Drupal\Core\Entity\EntityInterface $entity) {
  if ($entity-&gt;bundle() == 'salesforce_mapped_object') {
    $entity_info = $entity-&gt;get('drupal_entity')-&gt;first()-&gt;getValue();
    $type = $entity_info['target_type'];
    $id = $entity_info['target_id'];
    switch ($type) {
      case 'node':
        $node = \Drupal\node\Entity\Node::load($id);
        $node-&gt;save();
        break;
      case 'user':
        $user = \Drupal\user\Entity\User::load($id);
        $user-&gt;save();
        break;
    }
  }
}


Thanks to @leymannx in the above comment for the guidance.