Calling entity reference field in page template
The entity reference field normally contains just the entity ID as value.

Looking at Twig get value of field in entity reference and Drupal 8 loop entity reference fields.twig it seems a bit that

{{ node.field_name.entity }}


or 

{{ node.field_name.0.entity }}


or

{{ node.field_name[0].entity }}


might work.



If it doesn't work, try Twig Tweak which gives you some handy functions to print Drupal entities in Twig.

{% set nid = node.field_name.target_id %}
{{ drupal_entity('node', nid) }}


Or even easier as recommended by @4k4 in the comments:

{{ drupal_field('field_name', 'node') }}





  Twig Tweak is a small module which provides a Twig extension with some
  useful functions and filters that can improve development experience.