[@robin-w Moderator 7 years, 10 months ago]

function custom_bbp_sub_forum_list() {
  $args['separator'] = ';' ;
  return $args;
}
 add_filter('bbp_after_list_forums_parse_args', 'custom_bbp_sub_forum_list' );

or use

bbp style pack

to get the lists vertical