I've been out of the loop on foldable phones, and this is question is not related to specifically the iPhone Duo. How does it work that it doesn't show a crease in the middle? What's the breakthrough technology there? Or is there a visible crease?
I'll watch Marques when I want to get caught up on stuff like this, because he usually has a minimal fluff video on the subject.
For foldable phones, this might be a good pick to get caught up (5 months old, but minimal crease): https://www.youtube.com/watch?v=eFUB_jL_XcM
On the Samsung Flip you can definitely see a crease—it's not super annoying but it's definitely there
the lcd is flexible, it doesn't fold in a sharp crease but uses a complicated hinge to roll it into a loose bend when closed. But maintaining a "crease-free" appearance after many use cycles seems to be a major challenge in this market.
On other phones it is visible, here we’ll see soon.
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.
We'll find out when the hands-on reviews start coming in. Right now, we're seeing Apple's carefully-curated press photos & renderings