Widget recent comment filter by post meta_value

$post_args = array(
  'post_type'              => 'post',
  'posts_per_page'         => -1,
  'meta_key'               => 'field_name',
  'meta_value'             => 'field_value',
);

$post_query = new WP_Query( $post_args );
$posts_array= array();
if ( $post_query->have_posts() ) {
    while ( $post_query->have_posts() ) {
        $post_query->the_post();
        $posts_array[] = get_the_ID(); //Array of post ids
    }
    wp_reset_postdata();
}

//YOUR COMMENT ARGS SHOULD BE THIS
$args = array(
    'number'         => '30',
    'order'          => 'DESC',
    'orderby'        => 'comment_date',
    'post__in'        => $posts_array, //THIS IS THE ARRAY OF POST IDS WITH META QUERY
);

$comments_query = new WP_Comment_Query;
$comments = $comments_query->query( $args );

Don’t forget to update the test meta key and test meta value by your meta key and meta value.