I'm trying to do something like this yes - but I think I understand what the problem is.
In Firefox, when CSS scroll-snap is applied, when scrolled down, page is scrolled to the next section almost immediately, so the exit animations aren't visible. When I try your example in Chrome, there's a little delay between this actions - so animations are visible.
So for consistency - my question becomes, can I apply the full page snapping only with GSAP - so they will be consistent between browsers.
Thanks for your help by the way, much appreciated.