How to reveal a section by scroll?

No example unfortunately.

Sticky approach won’t work, as this just add a layer on top of an existing one.
https://benoitdelval.editorx.io/stick

I would like that an already displayed layer moves up out of the viewport, revealing the layer under which stays static. The revealed layer should be a container (with Progalleries inside), not an image with some parallax or reveal applied. The scrolling layer may be a jpg image.

Possible?

Thanks.
Ben