There will inevitably be a crease after a few weeks/months, as every folding phone has had. Apple is relying on Samsung's display tech, and Apple doesn't have better solutions than Samsung.

The reason it doesn't actively crease is because it's not like a piece of paper you press on to fold: the screen "rounds" itself, and as long as it doesn't go past a breakpoint (which is what the body of the phone prevents), it'll restore.