Display custom profile field in twig
This is a user template from Drupal 8. Check detail here or below code.

{#
/**
 * @file
 * Theme override to present all user data.
 *
 * This template is used when viewing a registered user's page,
 * e.g., example.com/user/123. 123 being the user's ID.
 *
 * Available variables:
 * - content: A list of content items. Use 'content' to print all content, or
 *   print a subset such as 'content.field_example'. Fields attached to a user
 *   such as 'user_picture' are available as 'content.user_picture'.
 * - attributes: HTML attributes for the container element.
 * - user: A Drupal User entity.
 *
 * @see template_preprocess_user()
 */
#}

&lt;article{{ attributes }}&gt;
  {% if content %}
    {{- content -}}
  {% endif %}
&lt;/article&gt;


Please see the comment code. If you want to render your custom field in template, just content.&lt;your_custom_field&gt;.
With your example is content.field_author_bio.

In case your field's content when rendering is not your expectation, you maybe need to use template_preprocess_user() for preprocessing content before rendering in the template (Search more about this function if you need).