Do 80% of millionaires own a used car? If yes, why?

Not for the main car, no.. because a car has to be reliable and safe. And used cars can fail in both these areas.

Probably most millionaires are business owners, so this means that they won't even own their own car, probably it's a company car, and therefore they benefit from depreciation and amortization and no VAT (sales tax). Some new cars with a discount and without sales tax are cheaper than used cars.

If it's true, it's probably simply because a 2nd hand car as described here https://www.meetrv.com/how-can-you-buy-cheap-used-cars-under-500/ offers more bang for the buck. I know a couple of people who are pretty well-off who consistently buy 2nd hand cars. You don't become a millionaire by spending your money recklessly; you become one by investing wisely. Because a 50K, ~3 year old car, is almost half the price of an equivalent new car, whilst retaining almost the same exact utility, with few, if any, additional running costs.