My cookies are set correctly to ensure they don't expire nor delete themselves, so no idea why DARK MODE is a constant, regardless of changing its setting in my User Profile. It never used to do this, I know that much.
Maybe the website has a curse on it. Did you cross paths with any practitioners of voodoo in the past?
Now THAT is a distinct possibility. Oh well, Light mode was originally the default but users rioted and forced us to make it Dark mode because Light mode is too hard on the eyes and causes brain damage.