The world is not generated by datapack but .json
It can be opened(or generated) in 20w30a but not 1.16.2 pre-1
MC-196593
world crash when the experimental world generate or open
Resolved
Invalid
0
The world folder structure for custom dimensions has changed in the pre-release: https://www.minecraft.net/en-us/article/minecraft-1-16-2-pre-release-1