Newly created fields are not being displayed
Adding a default value doesn’t actually set any value in the field. To do that you must either edit the nodes you want the field on and click save, or write an update hook that sets the field value on all the nodes.

An update hook must be placed in a custom module’s .install file, in your case it would be something like:

function MY_MODULE_update_N() {
  $nodes = \Drupal::entityTypeManager()-&gt;getStorage('node')-&gt;loadByProperties('type' =&gt; 'article');
  foreach ($nodes as $node) {
    $node-&gt;set('field_name', $value);
    $node-&gt;save();
  }
}


As @4k4 mentioned if you have to update too many nodes as you have memory to, you can create batch updates using the &amp;$sandbox, click here for more information