The biomes in the nether have got some issues. 

What I expected to happen was...:
I expected to head into the nether and find your normal, 1.16 nether.

What actually happened was...:

Instead, I found Crimson and warped forests with no trees, and soul sand valleys with a significant lack of soul sand.
Steps to Reproduce:
1. Start the game in 21w38a
2. Create a new world
3. build a nether portal, and go through it.