Do you have a character movement component? You could try setting the Gravity Scale to 0. You could also try setting your default land movement to Flying. I could be wrong, but I think Character (or character movement) class always applies gravity. If you’re not using Character, a different movement component will likely work better… or don’t use one at all.
There seems to be a “Planar Movement” section with “Constrain to Plane” checkbox and other settings. I’ve never used it, but might be something useful. Note that this shouldn’t be needed to stop your actor from falling. That should be fixed first.
I’ll try this in a separate project and will let you know. But you can try Gravity Scale to 0 in the meantime.