Add schema to yoast seo breadcrumbs

functions.php

<?php
/**
 * Add schema to yoast seo breadcrumb
 */

add_filter('wpseo_breadcrumb_links', 'jj_add_crumb_schema', 10, 1);

function jj_add_crumb_schema($crumbs) {

    if ( ! is_array( $crumbs ) || $crumbs === array() ) {
        return $crumbs;
    }

    $listItems = [];

    $j = 1;

    foreach ( $crumbs as $i => $crumb ) {

        $item = [];

        if ( isset( $crumb['id'] ) ) {
            $item = [
                '@id' => get_permalink($crumb['id']),
                'name' => strip_tags( get_the_title( $id ) )
            ];
        }

        if ( isset( $crumb['term'] ) ) {
            $term = $crumb['term'];

            $item = [
                '@id' => get_term_link( $term ),
                'name' => $term->name
            ];
        }

        if ( isset( $crumb['ptarchive'] ) ) {
            $postType = get_post_type_object($crumb['ptarchive']);

            $item = [
                '@id' => get_post_type_archive_link($crumb['ptarchive']),
                'name' => $postType->label
            ];
        }

        if(isset($crumb['url'])) {

            if($crumb['text'] !== '') {
                $title = $crumb['text'];
            } else {
                $title = get_bloginfo('name');
            }


            $item = [
                '@id' => $crumb['url'],
                'name' => $title
            ];


        }

        $listItem = [
            '@type' => 'ListItem',
            'position' => $j,
            'item' => $item
        ];

        $listItems[] = $listItem;

        $j++;

    }

    $schema = [
        '@context' => 'http://schema.org',
        '@type' => 'BreadcrumbList',
        'itemListElement' => $listItems
    ];

    $html = '<script type="application/ld+json">' . json_encode($schema) . '</script> ';

    echo $html;

    return $crumbs;
}

also change echo $html; to print_r($html);