I agree, but as long as the site follows my system settings I won't be needing a toggle at all. But I guess it should be there anyway.

I would point out that the "system" setting actually does have a special-use case: some users have their OS set to auto toggle from Dark to Light at a specific time (ie: sun down). Imagine how their daily flow is interupted by this? Especially since dark/light mode can be critically important nowadays with hands free night driving. A bright white screen can temporarily blind you.