I created a couple backups of my world to check out the new update and I'm glad I did.

Not sure what happened to generation in my world but I noticed a couple things:

Screenshot #1 - I've seen lots of the regular youtubers showing the biome blending when upgrading previous versions and mine is definitely not blending.

Screenshot #2 - Floor is at 0, I just jumped into spectator mode and dropped down and you can see it just stops at 0.

I don't think I need to toggle anything if I'm running the 21w40a version but maybe I missed something?

Thanks