Make Link to Comment Author Opens in New Window

Just open and edit your comment-template.php inside the wp-includes folder. Search the file’s source code until you find the function get_comment_author_link as below;

function get_comment_author_link( $comment_ID = 0 ) {
    $comment = get_comment( $comment_ID );
    $url     = get_comment_author_url( $comment );
    $author  = get_comment_author( $comment );
 
    if ( empty( $url ) || 'http://' == $url )
        $return = $author;
    else
        $return = "<a href='$url' rel='external nofollow' class='url'>$author</a>";
 
    return apply_filters( 'get_comment_author_link', $return, $author, $comment->comment_ID );
}

Now you only need to add target='_blank' inside the link tag, of the second $return variable;

$return = "<a href='$url' rel='external nofollow' target='_blank'>$author</a>";

Save the file and upload it to the wp-includes folder.