updatenode.php

<?php

$entityTypeManager = \Drupal::entityTypeManager();
$storage = $entityTypeManager->getStorage('node');
// Replace <article> with your nodetype.
$query = $storage->getQuery()
  ->condition('type', 'article')
  ->execute();
// Chunk in case you have thousands of nodes to update.
foreach (array_chunk($query, 200) as $chunk) {
  /* @var \Drupal\node\NodeInterface[] $nodes */
  $nodes = $storage->loadMultiple($chunk);
  foreach ($nodes as $node) {
    // Replace <status> with your field.
    $node->set('status', TRUE);
    $node->save();
  }
}