This is one way of doing it.
Add this to the extra.less template - specify the node IDs, comma separated, as required;
	
	
	
		Less:
	
	
		[data-template="forum_list"]
{
    .node--id
    {
        &2,
        &4,
        &8
        {
            display: none;
        }     
    }
}
	 
 
The node IDs can be obtained from the ACP -- 
admin.php?forums/main-forum.2/edit -- or via the browser inspector:
View attachment 256487