I just wanted to pop in and say that I found the following flag…
chrome://flags/#enable-force-dark
…enabled it, and am very pleased with the way that Brave forces web sites into a dark mode. In my limited experience, I feel like this feature is ready for primetime. I feel like this should be a side option next to the Dark mode setting.
I’m sure many people take features like this for granted. So I just wanted to give some recognition to whomever worked on this feature.
Nicely done!
Thanks for mentioning 
I found another one…
chrome://flags/#darken-websites-checkbox-in-themes-setting
This flag allows websites to automatically be put into dark mode or light mode depending on which theme your device was in.
I think this will be way better than the one you mentioned which force all website into dark mode, all the time.
I’m assuming that one just turns on or off a checkbox in the themes area. The checkbox itself probably turns the other one on and off without having to go to the flag directly.