It seems like soul sand is not spawning in soul sand valleys. The large bones and skeletons are surrounded by nether rack.

Btw, love the new mountains!!

What I expected to happen was...:
That soul sand would spawn in the soul sand valley biome.

What actually happened was...:
I could not find any soul sand in the soul sand valleys after searching them out in a creative world.

Steps to Reproduce:
1. Use world seed: -4363852756553760707 in snapshot 21w37a, in Java edition
2.  Go to the Nether
3.  teleport to soul sand valley at either: [1000, y, 1000] or [-48, y, 12]