from what i found arbeth is in the ethereum network so I thought it counted as ethereum because i found that arb are layer 2 ethereum
L2 used different blokchain but it's simply said that if arbitrum blockchain is connected to the ethereum blokchain since you can use ethereum address on arbitrum address. It means that if arbitrum is a ecosystem expansion from ethereum blockchain.
There are so many L2 blockchain. If you are still new and that's find if you have not yet fully known about that.
i have usdt on tether ethereum network
It means you need to bridge it to the arbitrum if you are willing to use it with cheaper fees to send and receive your USDT. You can try to swap your USDT to the WBTC if you are willing to do that.
It requires ethereum native coin to pay the fees.