Here is the pattern worth knowing before you move anything. A cashier lists Arbitrum, you deposit for a fraction of a cent, everything works. Then you win, open the withdrawal screen, and the only network offered is mainnet. Your cheap rollup deposit has become a mainnet payout, and the saving went back to the house.
Ubet documents this openly in its own help pages: USDT deposits on Arbitrum credit instantly, while withdrawals run on ERC-20 or TRC-20 because Arbitrum payouts are still in development. That is the honest version. Others simply present a shorter network list at withdrawal than at deposit and let you find out for yourself.
The other half of this trap sits on the bridge. Arbitrum, Optimism and Base are optimistic rollups, which means a native withdrawal back to mainnet carries a seven-day challenge period. So funds stranded on a rollup because the casino paid you there and your exchange will not accept it are not lost, but they are a week away unless you pay a third-party fast bridge to front the money.
None of this is a reason to avoid rollups. It is a reason to check both screens before the first deposit, which takes about thirty seconds and is the single most useful thing on this page. And with mainnet gas near a cent, a casino that only ever offers mainnet is no longer punishing you for it.