Well, on Polymarket they’re betting the USDC “stablecoin”, which must be bought for US$ (or else by exchange of other cryptocurrencies at the current market price) and is supposed to be redeemable for US$ if you go through the hoops to setting up an exchange account, link to a bank account, and all of the “know your customer” folderol required. So, to the extent that a tethercoin is real and retains its 1:1 peg to the US$, people are betting real money. This is presumably a way to get around the U.S. federal and state bans on “online gambling”, which define real-currency prediction markets within their prohibition. The only two prediction markets currently open to U.S. nationals are the university-operated PredictIt (based on New Zealand) and Iowa Electronic Markets, in…you guessed it…the U.S. state of Iowa. Neither, at this writing (2023-07-27 at 22:40 UTC), appear to have markets on replication of the claimed room-temperature superconductor.
Requiring participants in a prediction market to first get into cryptocurrency is going to dramatically reduce the breadth of participation and the liquidity of the market and its efficiency in establishing the probability of the prediction from the crowd. I would also doubt that operating a prediction market in the U.S. in a stablecoin is going to evade attacks against it as online gambling once its size grows sufficiently large to come onto the radar of state and federal “no fun of any kind” agencies.