You just need to make it obvious that saving these preferences will cause some state to be written to the client browser, and not use this state for any other p

You just need to make it obvious that saving these preferences will cause some state to be written to the client browser, and not use this state for any other purpose than what the user consented to. Placing a “these preferences will be saved in a cookie” next to the respective save button is enough. Cookie banners aren’t a requirement, they’re a legal consultant meme with a dash of dark patterns.