No demo account like it is in forex, not common in crypto. I have seen demo account on OKX, you can try it, but I am not sure it is for future trading and also possible to have different layout.
My advice is that you can use small amount of money for future trading, I remember I used less than $1 to open long and short positions on Binance several times before I started real trading, though it depends on the leverage used, if using lower leverage, the amount of money needed to open a position will increase, but I think $10 is enough for 1x leverage.