Dishwashing soap will break down the wax on your car that protects the paint. If you like to wash your car a lot, it really is not good to use it on your car.
On a deck dish soap would be too bubbly, and on the deck you might need other chemicals. Deck washing sometimes does not need any chemical, just a pressure wash. I would pressure wash.
Maybe you can use Murphy’s oil soap? I am not sure, but if the deck is stained and sealed maybe that would work.