Argentine here. Italian bidets are just a sink you can sit on, with a faucet on the rear. You clean yourself using your hands. Argentine bidets are also a sink you can sit on, but they have a shower pointing up to your rear. There's basically two ways to go: don't use your hands down there and let the water pressure do its thing, then go back to the toilet and dry with TP; or use your hands and soap and dry with a towel.
In any house you go, you will see soap on the bidet… So I'm probably not an outlier in using soap.