It's been behind a flag for ages. Maybe because of performance issues?

Enabling (layout.css.scroll-driven-animations.enabled) and refreshing the codepen gives a "we crashed this to prevent a crash from an infinite loop" clicking to allow the infinite loops allowed me to see the animation.

Fedora 44 Kernel: x86_64 Linux 7.0.10-201.fc44.x86_64 Firefox 151.0.2