If your goal is making money, then that's different. I personally don't encourage people to get into the betting aspect unless you don't mind paying my rent, know what I mean? It's one of those "if it was easy everyone would be doing it" things. The limits on bet sizes only matter once you can demonstrate long-term profitability, IMHO. Since prediction skills are still applicable to basically everything, you're not 100% wasting your time just by testing your abilities on gjopen.com.
If you want intellectual engagement and don't prioritize money, then you can find markets on any topics. Which is why I suggested gjopen.com, and if you are good enough then they will try to recruit you to their analytics platform.
But, yes, politics via PredictIt has been the standard CFTC-approved platform. They're rumored to be working on a more general uncapped platform due to competition from Kalshi (next paragraph).
A new YC startup, Kalshi.com, got CFTC approval for uncapped markets with no topic limitations. They only got up and running last year, so often the markets don't play as large with no betting limits even compared to PredictIt. We're hoping they get momentum, but they could be ahead of their time and give up before more widespread adoption takes off.
There is also Polymarkets.com, but it's trying to operate the markets via blockchain. It's often not the greatest user experience for that reason, but they get more leeway on markets and are uncapped.