LPT: If your phone is still too bright at the lowest brightness setting, reduce the white point of your display in settings.

For example, if you’re using your phone before bed or otherwise in a setting where you need your eyes to be adjusted to total darkness, (for iPhones) open Settings and go to General>Accessibility>Display Accommodations (similar settings exist for other electronics, but I️ am not familiar)

Edit: You can add a shortcut where a rapid triple-click of the home button lowers the white point to your preset level. To do this, go to General>Accessibility>Accessibility Shortcut, then select "Reduce White Point". Infinite thanks to u/jokingnuthatch