Try this Reshade preset.
https://www.nexusmods.com/baldursgate3/mods/2011

I have made it without knowing that early versions were better in graphics. That preset is very simple and fast. If you want the game to be trully dark download v1.1.0 and turn off "Eye Adaptation" shader. Version 1.2.0 is lighter and has different shadow-midtones-highlights preferences. But it has a cinematic appearence.