Nonsense.
You are correct that people keep stating such things. But it is incorrect.
That example would be an essential cookie, also known as a strictly necessary cookie.
A shame this FUD is still being spread.
That's not what various references (and AIs) say. Strictly necessary means strictly necessary. They didn't bother defining it in the law. However, user preferences were called out specifically in the WP29 opinion as something that wouldn't count as strictly necessary if scoped any wider than the browser session. So if the plain English meaning and the drafters' opinion contradicts your opinion, why should I risk significant fines to trust it?