Arbitrum’s native token is ETH, not ARB.
It seems that recently a token called ARB was created. But it seems that this is a governance token and not a native token.
In other words, when swapping between tokens on the Abritrum blockchain with Uniswap, etc., you need “ETH on the Arbitrum One chain” instead of ARB. It’s confusing, isn’t it?
Also, when swapping on the Arbitrum One chain, the gas fee is cheaper than the Ethereum chain, but still expensive compared to Polygon or Celo.