The double zero exists in American roulette. The double zero is a double advantage for the Casino, so that the house advantage increases noticeably. The players lose their bets not only on the "single" zero, but also on the double zero. This means that there are then two numbers in the Pot where the entire stakes are retained by the casino.
Meanwhile, there are even special Roulette tables with the name "Double Zero Roulette". Basically, however, gambling enthusiasts should avoid such gaming tables because of the double house advantage. While this is 2.6% at a "normal" roulette table, it is 5.2% with a double zero. In German-speaking countries, there are hardly any roulette tables with a double zero in the local casinos.