For prediction markets you can find out who the insiders are for different categories over time, see for example:

https://x.com/peterjliu/status/2024901585806225723

But there is still the problem of knowing which new trades the insiders made before the bet is settled (maybe solved by being an insider of the prediction market), and also since prediction markets need money on both sides (you are betting against other people, not the 'house') when the insiders make their buy they probably eat up most of or all of the action on the other side.