The issue of bribing/threatening a sports player to throw a game has existed for over a century. It's not a new problem. The only thing special about Polymarket is the expansion of surface area.
My preferred solution would be to just ban it all, or if you really want to allow sports betting only allow betting on the outcome of events happening in the venue one is physically in.
The existence of sports betting absolutely encourages people to throw matches and the existence of X betting absolutely encourages people to try to make X come about.
Strong regulation and legal consequences could potentially fix this. We don't see tons of people shorting a company and then bombing that company's HQ.