How to build render array with node title linked to node for a list of nodes
As pointed out by @4k4 I used the entity reference field formatter, which does not apply here. Theming as link, as answered in How do I theme a link? does the job:

if ($teaser_display) {
  $value = \Drupal::entityTypeManager()-&gt;getViewBuilder('node')-&gt;view($node, 'teaser');
}
else {
  $value = [
    '#type' =&gt; 'link',
    '#title' =&gt; $node-&gt;label(),
    '#url' =&gt; $node-&gt;toUrl(),
    '#cache' =&gt; ['tags' =&gt; $node-&gt;getCacheTags()],
  ];
}