Reference current user when creating a content type
You can set default values in a hook_ENTITY_TYPE_create:

/**
 * Implements hook_ENTITY_TYPE_create() for 'node'.
 */
function mymodule_node_create(\Drupal\node\NodeInterface $node) {
  if ($node-&gt;getType() == 'my_content_type') {
    $node-&gt;field_user-&gt;target_id = \Drupal::currentUser()-&gt;id();
  }
}