interested to see if this makes any difference

content-visibility

The content-visibility CSS property controls whether or not an element renders its contents at all, along with forcing a strong set of containments, allowing user agents to potentially omit large swathes of layout and rendering work until it becomes needed.

contain-intrinsic-size

Using auto to reduce rendering cost of long pages

The following example shows the use of auto to skip painting and rendering of off-screen sections. This helps with both load and interactions on the page, since the content outside of the viewport is not rendered.

<style> section {   content-visibility: auto;   contain-intrinsic-size: 0 500px; }