You might want to try putting the "Extra dim" option in your quick panel drop down. It's adjustable, so you can make the screen extremely dark. I use this quite frequently. Another option, if you switch between dark and light mode often, is to create a routine that automatically lowers the brightness whenever you switch to dark mode.
Dark mode doesn't effect brightness levels, it just forces a dark color scheme. Brightness will still need to be controlled manually if you want to keep it darker, although if you leave autobrightness on and continually reduce the brightness it will learn to keep it on a lower setting.
