though I believe professional sport players aren't allowed even to do that (whether because they might still have inside information - say, a teammate is recovering from injury faster than publicly known - or just to discourage betting which has been a personal problem in sporting types, I'm not sure). You might say that internal polls could give a similar unfair advantage, though. They should at least be willing to say in public when they do "I've just bet on myself to win - I think we have a better chance than the bookies say".
But the bets on timing of elections, or on your opponent to win, just look like cheating.
I wonder when people will bring up Sunak's bet with Piers Morgan about sending asylum seekers to Rwanda. Sure, it was for each to nominate a charity (Morgan has already claimed victory, and nominated the British Red Cross), and it was indeed in public, but it might be good for someone to mention it and see how Sunak tries to justify what he did.
Oh, I hadn't seen this - Sunak has tried to say the one guy who they paid to go there means the bet was off: