graphql_custom_meta.php

<?php
add_action( 'graphql_register_types', function() {
    register_graphql_field( 'Album', 'externalLinks', [
       'type' => 'String',
       'description' => __( 'Links to the album on external services', 'smolblog' ),
       'resolve' => function( $post ) {
         // Get the meta field
         $links = get_post_meta( $post->ID, 'find_links', true );

         // Return an empty JSON object if the meta field is empty
         if (empty($links)) {
         	return '{}';
         }
         
         // If $links isn't an array (there's only one link), make it an array.
         if ( ! is_array( $links ) ) {
         	$links = [ $links ];
         }
         
         // JSON encode the array and return it
         return wp_json_encode( $links );
       }
    ] );
  } );