Yeah but that requires cookies. Not everybody allows them. I block everything that isn't a first party cookie, and set them to delete every time I close my browser.
To be fair though, "The website doesn't remember my settings because I don't let it," isn't really a problem the website can solve.
I just had a thought that I'd like to see a plugin that independently remembers whichever cookie-based settings you want it to on a per-site basis and then re-inserts those settings into fresh cookies whenever you visit using some sort of search & replace or markup interpeter. Basically a way to maintain personal control over what data cookies can hold.
maybe it'd be nice if we just had "config registers" alongside cookies that just allowed us to store a single bytes worth of information in it or something. Would be perfect for things like darkmode.