I was going to say it should respect the system setting. Apparently that’s a problem. But personally, i find it irritating if something can, but doesn’t respect my system setting, and i personally fought to not include such a toggle on an iOS app. At least on iOS, if you set things up correctly, it’s easy to support the system setting, and implementing a toggle makes things harder but i am not a web developer, so won’t comment on the problems there.

I’ll add that on iOS, you can add the light/dark toggle to that drop down from the top right drag down menu. In most cases, i use dark mode anyway, i find the need to change the mode because something looks terrible in one mode or the other to be few and far between, but sometimes, i like to work outside, and just switch to light mode. And if i have to find another toggle because something didn’t respect that, it is irritating