How to modify field value in other nodes after node update?
Use hook_form_alter or hook_form_FORM_ID_alter
Add a custom validation that runs after all validation has passed
$form['actions']['submit']['#submit'][] = 'mymodule_update_referenced_nodes';

Then in that function
function mymodule_update_referenced_nodes(&amp;$form, \Drupal\Core\Form\FormStateInterface $form_state){

  $field_other = $form_state-&gt;getValue('field_other')[0]['value'];

  $references = $node-&gt;get('field_referenced')-&gt;referencedEntities();
 
  foreach ($references as $referenced_node) {
    $referenced_node-&gt;field_other-&gt;value = $field_other;
    $referenced_node-&gt;save();
  }

}