But this means you're "abusing" dark/light mode to signal unrelated information. If some visual customization (theme, font size, etc.) happens to allow you to do something like that, then of course more power to you, but I don't think it has any relevance to the design of the thing itself. It just seems unreasonable to me to expect designers to consider all the ways their designs could do double-duty for any given user (cf. "every change breaks someone's workflow").

I was just supplying one reason for changing it, other people may just prefer some particular site or application in light mode versus dark (and vice versa) instead of managing multiple instances of the same thing like I am. Suppose you're editing documents and your word processor has dark mode, but you want it to always be in light mode. With the described control in the article you would have to change the behavior in the evening, specifically, to get it to stay in light mode permanently (or change your system settings to be opposite your normal settings, switch it to light, and then switch your system settings back).

There is no way any one with any common sense can think that this two-choice option (one is magic, one does what you would expect; which is which depends on time of day for many users) is better than a three-choice option where each choice does exactly what you'd expect.