If you want to disable replies in specific bbPress forums, use the following code snippet. This will allow you to control which forums permit replies:

<?php
function disable_forum_replies( $forum_id ) {
    if ( $forum_id == 5 ) { // Replace with your forum ID
        return false;
    }
    return true;
}
add_filter( 'bbp_allow_reply', 'disable_forum_replies' );

This code will disable replies in forum ID 5. You can change the ID to match the forum you want to restrict, while keeping replies active in other forums.