Fixed-wing flight is one. I remember that being a point in the aviation exhibit at the London Science Museum. Nothing was stopping people from building hang-gliders in at least the Renaissance, maybe earlier? But everyone was fixated on flapping wings.
I think one of the Assassin’s Creed games plays with the idea, having Leonardo build a hang-glider for the main character.
One of the Wrights' enabling technologies was the powered fan that allowed them to make a wind tunnel to refine the airfoil from barely-functional to fairly-useful. They used a small gasoline engine, which enabled them to construct their wind tunnel on a small independent budget. I suppose you could have done that on an institutional level as early as 1750 with steam engines (or perhaps earlier with water power) but mines and mills and factories weren't particularly interested in the problem.
I think one of the Assassin’s Creed games plays with the idea, having Leonardo build a hang-glider for the main character.