Your electric bill won't be reduced by playing two games on one computer instead of two computers with two games if that's your end-goal. In the end, you'll still consume the same amount of electricity more-or-less. However, you can make it cheaper if you use something like a laptop and run on the lowest setting while in tray but obviously you can't run the game on the laptop and on your pc using the same account. You can run as many accounts as you like on as many computers as you desire on the same network, no one cares about that because everyone has their own situation ie: there are plenty of couples who play the game.

I have a 3080 and soon the other computer will get a 4070TI so i expect the bill to go even higher. I feel you lol But in general it's not worth fishing or doing AFK anything overnight at the cost of current electricity. Back when crypto mining was viable, people would mine for crypto instead of AFK and then use that money from mining to buy in-game outfits. Obviously those days are long gone :P