bbPress.org

I believe that wordpress support forums use bbpress, how can I add this “Add New” button to my bbpress forum

they do , the bbpress standalone version

suprisingly this button is not in here.

wordpress.org use a customized version of bbPress just like this site ooes

you can try something like this

<?php if ( bbp_is_single_topic() ) : ?>

<?php if ( is_user_logged_in() ) : ?>
<a class="bbp-new-reply-button" href="#new-post">New Reply</a><li>
<?php endif; ?>		
	
<?php endif; ?>

place the code in loop-replies.php above the <li class="bbp-header">

you can style the link like so with some CSS , place wherever you place custom CSS

.bbp-new-reply-button {
    background:black;
    color:#fff;
    text-transform:uppercase;
    text-decoration:none;
}