Layout

The host gets pointer-events: none, and position: relative if it was static. Every layer inside is absolutely positioned. Keep the host empty.

Backdrop Root

A backdrop-filter only sees as far back as its backdrop root, so nothing between the host and the content can have opacity below 1, a filter, a mask, mix-blend-mode or will-change on those. Put the host beside the scrolling content, not inside a faded wrapper.