Something else: It’s not only the huge energy demands, but the physics of moving that much air. Even if the Back to the Future flying car were real because of a working, compact fusion power plant like Mr.Fusion it would still be impractical as a domestic car because the enormous air blast it created on takeoff and landings would cause damage to any unsecured nearby objects.
And even if the Mr Fusion unit itself operated completely silently the air blast it generated would be deafeningly LOUD!** The majority of most all aircraft’s noise comes from it’s propeller/rotor, not its engine. So you’d not only need a breakthrough in power generation you’d need something even more inconceivably out-there, namely some kind of anti-gravity…