The main problem with this being a “mode” is that I don’t want it in 100% of cases. For instance, on the Mac it was originally possible to darken only the menu

The main problem with this being a “mode” is that I don’t want it in 100% of cases. For instance, on the Mac it was originally possible to darken only the menu bar but now that is only allowed if everything is dark. Frankly, in many cases it makes more sense to mix these effects, e.g. it might also be nice to have darkened sidebars in lighter windows. Another reason I don’t want it on all the time is because a lot of things still have really terrible Dark themes, to the point of being eyesores. It is amazing how much more the choice of colors matters in dark themes, and if this is wrong it is almost unusable. Some web sites had long used primarily-light or primarily-dark themes, and it is now weird that some of them try to “adapt” to your dark/light “mode”. Frankly, it usually looks worse when they switch to their less-refined alternative and I would rather they either put a lot more effort in to both themes or just keep the original look in all cases.