The iPhone Duo's squat, tablet-like outer display is a compromise, and a book-shaped foldable may lack wide appeal; its right-side UI bias is akin to a book (John Gruber/Daring Fireball)
Apple started with a title card that said “The following was shot on iPhone”, but the whole keynote — including the fun fake-movie openings — was shot on iPhone 18 Pros.
We haven't written up this one. Techmeme has the full story — the link below goes straight to it.