Anything that moves, flashes, or makes sound needs an off switch and a safe default. The platform already tells you what the user wants: honor it, and do not invent your own guess.
About 1 min of reading
Make motion opt-in instead of opt-out
Find the animations
Before you run it, say out loud what it will print. Then open the answer.
Wrap them
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Bump the token
Before you run it, say out loud what it will print. Then open the answer.
Test with the OS setting
Before you run it, say out loud what it will print. Then open the answer.
Ship no motion, then add motion only inside the media query. That way a browser that does not support the query gets the calm version, which is the safe direction.
It does not cover parallax, auto-advancing carousels, or a timer that forces an action. Those need their own pause controls, and the media query is not enough.
@media (prefers-reduced-motion: reduce) wraps the animation rules. The user's operating system made that choice; your job is to read it, not to ask again.
Anything that flashes more than three times per second must be stoppable and must not flash for more than a second. A pause control is required, not optional.
Audio that starts without a user action needs a visible way to stop it on the same page. The cheapest fix is to not autoplay at all.
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