For example, if the user adds $100 to his ETH account and only withdraws $70, after a $20 commission, he is left with $10 on his account that he will never get to use.
Therefore, we need to find a solution that will allow us to generate separate user addresses for monitoring and deposits. This should enable us to get all the funds in one wallet, leaving no leftovers.
When you send 70 btc from an address with 100, the change usually goes to a change address. This might be the case.
However, AFAIK , ethereum doesn't work like this and there is no change address as there are no utxo.
BTC has a solution that allows us to create subaccounts, but what should we do with the other coins?
Ethereum also has this option to create sub accounts, which is basically a new address
https://ethereum.org/en/developers/docs/accounts/