When there is more than one dark color scheme that is user selectable, the two drop downs appear and the toggle icon shows.
When there is only one dark color scheme that is user selectable, the Dark drop down disappears and instead, the “automatic dark mode” checkbox appears.
When a user thinks “Hey, I don’t want it to be automatic, I want to use the toggle” and deselects the “automatic” checkbox, the toggle disappears.
So to get the manual toggle, you have to enable automatic switching. 