I think what you’re missing is that the entire Earth is the reaction mass.

I’ve had a bit of fun doing the maths on space launch systems that function like this — if I remember right, you might even be able to do it… if you can make a monocrystalline superconductor, of whatever the best critical current density was about five years ago, about ten times the combined mass of your payload and cooling equipment.

Unfortunately there are limits on which direction this force can act in that make it even less useful than I’ve just made it seem.