I know this mod is very early into development but I'll like to point out that End's Phantasm's biomes doesn't show up on all Nullscape's biomes including the revamped vanilla ones when using /locate. Though the fallen stars do work as intended.

1.20.1 and 0.1

from what I'm it seems to be affecting both forge/fabric ports of the mod

What version of mod and Minecraft did you try?

well, will try to fix that in next forge release

okay i know i'm super late but that's due to nullscape completely overriding the end.
A way to fix this is to edit nullscape's files by making a datapack either to add the dreaming_den as a biome or by changing phantasm's is_dreaming_den biome tag to include the vanilla end highlands (so it gets all the biome's features)