I am trying to displaying VERY Special Characters (like
As discussed in comments.
In many cases, you need to place all of the code following
$db->query("SET character_set_results=utf8mb4"); before that line.
Also using a different file encoding could also help.
I've had to do that myself before, oddly enough. It could also be the server's default encoding that may be overriding something, somewhere; I've had that problem before also.
Plus, if you're querying somewhere, as in doing a SELECT, UPDATE or INSERT, then it is important that the encoding codes are placed before the query, should that be the case.