add preferred source

function jnews_add_preferred_source_after_content( $content ) {
    if ( ! is_singular( 'post' ) || ! in_the_loop() || ! is_main_query() ) {
        return $content;
    }

    $domain = wp_parse_url( home_url(), PHP_URL_HOST );

    if ( empty( $domain ) ) {
        return $content;
    }

    $preferred_source_url = add_query_arg(
        'q',
        $domain,
        'https://www.google.com/preferences/source'
    );

    $button = sprintf(
        '<div class="jnews-custom-preferred-source">
            <a href="%1$s" class="jnews-custom-preferred-source-button" target="_blank" rel="noopener noreferrer">
                Add us as a Preferred Source on Google
            </a>
        </div>',
        esc_url( $preferred_source_url )
    );

    return $content . $button;
}

add_filter( 'the_content', 'jnews_add_preferred_source_after_content', 20 );