There's a lot of new things in such a small update... well done Mojang! Here's a list of what they've shown in the newest 24w40a snapshot:
1. Pale Garden Biome

2. Pale Oak Tree

3. Pale Moss Block

4. Pale Moss Carpet

5. Pale Hanging Moss

6. Creaking Mob & Creaking Spawn Egg

7. Creaking Heart Block

The Pale Garden is a biome variation of the Dark Forest where all of these new blocks are obtainable at. Be prepared though - there's apparently new ambient sounds... Just don't go there during the night time.
These sounds are not coming from the biome itself, it's generated by the blocks that are within that biome.
For servers owners, there's a brand new /rotate command! This allows you to rotate entities to your liking - let your imagination shine on this one. What could this be used for?
You are able to try out the new update on a server with your friends as well. Download the snapshot for your server here! Remember to toggle the "Winter Drop" experiment on for it to show up.
Happy exploring!