What Polymarket says on the topic (https://integrity.polymarket.com/) is that they do not surface insider information and you mustn't trade if you have any.

Because the prediction market community is filled with liars and fraudsters, of course, it does seem to be common knowledge that this restriction isn't meant to be taken seriously, much like Polymarket's fake rule that Americans aren't allowed to use it.

But once you start from the premise that everything prediction markets say about their rules and practices is a lie, why should we believe they provide any genuine signal for anything?