I really like the fact that your "recipe" already includes support for prefers-reduced-motion. Parallax can really trigger motion sensitivity issues up to vomiting or several days of bed rest with severe migraine.
You did leave that part out of your recipe though. Would you mind adding it there, so that people who copy paste are more inclined to actually keep/use that part as well?
Edit: if the body has class="no-sda", it uses a js fallback.