catter1
commented
4 months ago Terralith is a datapack (yes, even the mod version - it is a datapack packaged as a mod). Due to this Minecraft bug, worldgen datapacks cannot support other world types, such as Large Biomes, Amplified, or in your case: Superflat. Although it is a pain, you will need to disable Terralith when making and using superflat worlds. This will be the case until either Mojang fixes the bug, or we spend a long time custom coding a mod to fix that.
What Minecraft version(s) does this apply to?
1.20
Project version
2.4.8
Mod or datapack version?
Mod (Forge)
Describe the bug
When trying to generate a flat world, the default world type will be generated
Additional context
No response