Our understanding right now is that gravity is the shape of spacetime. As the modification of spacetime even on a small scale involves huge masses and thus energy, it doesn’t seem possible to modify our local spacetime in a useful way without seriously messing stuff up. It’s like removing the Earths gravity, by removing the Earth. If you’d use just a fraction of that energy for a rocket, you’d get a lot further. So unless we are really really wrong about gravity (which we might be, but not likely), anti-gravity is not a thing.