This company has been selling detail supplies since 1971, and still sells many of the same vinyl protectants and stuff people have been using forever. https://mark-v.com/

Locally the detail shops will spray diluted vinyl treatment under the hood and let it soak into the plastic after the engine compartment has been pressure washed. When you go to a a car lot and buy a trade-in that has been detailed and all the stuff under the hood looks new that is what has been done to it to make it look that way. Drive some miles on a dusty road and it will collect dust and look like a chocolate powdered donut.