wp-api-blocks-callback.php

<?php

add_action('rest_api_init', function () {
    !function_exists('use_block_editor_for_post_type') &&
        require ABSPATH . 'wp-admin/includes/post.php';

    $postTypes = collect(
        get_post_types_by_support(['editor'])
    );

    $postTypes->each(function ($postType) {
        use_block_editor_for_post_type($postType)
        && register_rest_field($postType, 'blocks', [
            'get_callback' => function (array $post) {
                return parse_blocks($post['content']['raw']);
            }
        ]);
    });
});