How to render taxonomy field_custom in page--taxonomy--term.twig?
You need to prepare the Twig variable in a preprocess hook:

function mytheme_preprocess_page(&amp;$variables) {
  if (\Drupal::routeMatch()-&gt;getRouteName() == 'entity.taxonomy_term.canonical') {
    $term = \Drupal::routeMatch()-&gt;getParameter('taxonomy_term');
    $variables['field_example'] = $term-&gt;field_example-&gt;view();
  }
}