How can I have multiple content types pick up the same template?
Normally you'd simply use node.html.twig and then have different node templates for other node types. But I can imagine that it can make sense to bundle certain node types differently instead of providing distinctive templates for all other node types.

So you can implement hook_theme_suggestions_alter or hook_theme_suggestions_HOOK_alter to provide an extra template suggestion. The following snippet lets nodes of a given type pick up a node--foobar.html.twig template if present.

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function MYTHEME_theme_suggestions_node_alter(array &amp;$suggestions, array $variables) {

  $bundles = [
    'contenttype1',
    'contenttype2',
    'contenttype3',
    'contenttype4',
    'contenttype5',
  ];

  /** @var \Drupal\node\Entity\Node $node */
  $node = $variables['elements']['#node'];

  if (in_array($node-&gt;bundle(), $bundles)) {
    $suggestions[] = 'node__foobar';
    $suggestions[] = 'node__foobar__' . $variables['elements']['#view_mode'];
  }
}