But we have formulas that are checked and double-checked? How could it not be a force? Gravity is not a force, it is a space-time distortion caused by the presence of mass. In other words, if you put two masses in relative vicinity there won’t be a force that attracts each one to the other mass, but the space will warp in such a way that those two objects will move towards each other.
Newton found out that this space distortion is working based on formula F = G M1 M2 /r^2, but Einstein was the one to tell, in General Relativity, that the presence of mass distorts space-time.