It seems you are confused between futures and cex/spot if you are going to futures there's no list of pair for USDC to USDT because these two coins are stable coins. Even in other exchanges, you can't find this pair because both of them are stable coins. Unless you trade on spot/cex to place a limit order, you can also directly convert USDT to USDC and vice versa.

Take note of futures. If you are going to use it when buying something in futures, you won't get any coins; instead, you will end up placing a buy or sell position, so be careful because if your position liquidates, you will lose all of your funds in an instant.