As some folks may or may not know, there is now an "Extra Dim" toggle in the Quick Settings panel.
If you use "Eye Comfort Shield" (I do, every evening) to dim the screen when your surroundings are low-light (or no light :)), Extra Dim turns down the "dimness" even further.
But Extra Dim is not just an On Off toggle - there are additional settings - and you can access those settings a couple ways.
a) Pull down to show the Quick panel and swipe until you see Extra Dim ... long press it and you'll be automagically taken to the Extra Dim configuration.
b) (phone) Settings, tap search icon, type "dim" and you'll see Extra Dim under Accessibility - tap it
I've attached a screenshot ... you'll see there are settings for:
* Extra Dim Shortcut (places a shortcut floating icon on the Home screen)
* Intensity (default is lowest (least dim), which I've adjusted to "most" as seen in screenshot)
* Turn Off after Restart