Having 12 or more biomes in a dimension removes the fog if effects is set to The Nether.

You will see the difference between these 2 datapacks. 

1. Create a new world
2. Install the Dream 11 datapack
3. Teleport to the "dream_dimension"
4. Look around and it  should have the fog as expected 
5. Then, create a new world with Dream 12 datapack
6. Teleport to the "dream_dimension"
7. Look around - no fog