Drupal - Attach library to a specific page

If you're using a twig template, you can add it there.

{{ attach_library('module/library') }}

Which is helpful when you want to control whether the library loads before or after the content.

https://www.drupal.org/docs/8/theming-drupal-8/adding-stylesheets-css-and-javascript-js-to-a-drupal-8-theme

You have to attach the library to block content, hopefully code below should help

$build['#attached']['library'][] = 'module/library';