This effect is built using a 3-layer architecture:
A tall container (300vh) that provides the scrollable area. It acts as the "track" for the animation timeline.
A sticky container (100vh) that holds the Background Image. It stays fixed in the viewport while the user scrolls through the outer track.
A wide element (200vw) that moves horizontally. Using
mix-blend-mode: screen, its Black Text becomes
transparent to reveal the middle layer's image.
↓ Scroll down to see how they interact ↓