As far as I am concerned, that component is outdated and doesn’t support the new dark theme feature.
Also in our use case we don’t have any extra space in our mobile header, so we prefer the user menu.
That toggle doesn’t make use of the core dark mode functionality, doesn’t it? See the corresponding topic here, the component hasn’t been updated in a while:
No, it doesn’t make use of the dark color scheme you can set in the admin backend. It uses new css rules for it’s own dark scheme. So the name is a bit misleading, because it switches only to the Alien theme dark colors.
I’m not aware there’s a generic theme component to toggle color schemes right now. I guess it could be written similar to the Header Theme Toggle and using functions from discourse/lib/color-scheme-picker. Can’t code it myself either though