Not sure what you mean by "not something you dictate to the server", browser preferences are client-side. When you say "all of those settings" there's really two major prefers- settings and you already covered one (prefers-color-scheme), writting an extra query to cover prefers-reduced-motion requires minimal effort and provides a lot of value to your site's accessibility.

This is CSS, it's not dictating anything to the server, rather to the browser.