I'm not sure what you mean by "vacuum buoyancy." Were you thinking about the answer at Newton?

There is nothing exotic about vacuum buoyancy as it's described there. For example, if you have a submarine filled with air, it will float (be buoyant) as long as its total weight is less than the amount of water which would fill the same volume. Removing the air from the submarine doesn't change the weight of the submarine much, maybe a kilogram (a couple of pounds). Density is what matters most for buoyancy. Hydrogen gas in a balloon gives almost as much buoyancy in air as a perfect vacuum would (93%). The vacuum isn't what causes a submarine or a balloon to be buoyant, but the pressure of the water around it.

For the moment, we don't really have any idea what dark energy even is, apart from the fact that the universe seems to be accelerating in its expansion as if some anti-gravity-like force were at work. Some theoretical physicists have come up with some explanations, but there are no data that I know if to support any of these theories, let alone a practical application for it. These theories also will depend upon mathematics that is far beyond the high school or even the college level.