The window.scrollY is a problems!

[Weibozzz]

your code

const getScrollToBottomValue = (): number => {
   if (!childrenRef || !childrenRef.current) return -1;
   const scrollTop = window.scrollY; // is the pixels hidden in top due to the scroll. With no scroll its value is 0.
   const scrollHeight = childrenRef.current.scrollHeight; // is the pixels of the whole container
   return scrollHeight - scrollTop - window.innerHeight;
 };

The window.scrollY ！It is limited to being used only in the window. If a scroll bar appears at a maximum height on its outer layer, it will not work