Update the default preview link

update_preview.php

<?php
add_filter('preview_post_link', array( $this, 'wp_gatsby_preview_setup_preview_link' ));

public function wp_gatsby_preview_setup_preview_link() {
  $site_url = 'https://mygatsbysite.com';
  $id = get_the_ID();
  $post = get_post($id);
  $slug = $post->post_name;
  $post_status = $post->post_status;
  $nonce = wp_create_nonce( 'wp_rest' );
  $pt = get_post_type_object(get_post_type());
  $post_type = str_replace('_', '-', get_post_type($id));
  
  $link = $site_url.'/blog/'.$slug.'?id='.$id. '&_wpnonce='.$nonce.'&preview=true';
  
 return $link;
 
}