I've never seen anyone do that until yesterday. So I wanted to know is this appropriate for when preparing apples for any meal, how about other fruits? Unlike plates, fruits can absorb chemicals.
No, you would not use a detergent or soap when washing fruit.
Normally, you would just wash them with water, using a brush on thick skinned produce.
See, for example, Best Ways to Wash Fruits and Vegetables from the University of Maine extension.
Yes, I've done it for decades using unscented, clear dish detergent (such as Seventh Generation). Just a tiny drop with lots of water.
Just soak your fruits in mild hot water and that should take out any residual items on the fruit
I suggest using an unscented liquid castile soap like Dr. Bronner's. It is all natural and non-toxic. Unscented commercial dish liquid can still contain toxic chemicals and preservatives, even 7th Gen.