If you wish to disable the search feature on bbPress forums, use the following code snippet:
<?php
function disable_bbpress_search() {
if ( is_bbpress() ) {
remove_action( 'bbp_template_before_forums', 'bbp_forum_search_form' );
}
}
add_action( 'wp', 'disable_bbpress_search' );
?>
This will remove the search form from your forums, preventing users from searching for topics.
