Related to MC-610 (may be this bug is duplicate of it). But in this bug, grass place on sculk generate in deep dark Single Biome world.

Steps to Reproduce:

Step 1: Create a world with World Type: Single Biome, set it into Deep Dark.
Step 2: When spawn in, look around for grass on sculk (while looking for them, you may find half floating tall grass, see MC-256103 for more info)

Seed: -2685110850896552896
/execute in minecraft:overworld run tp @s -95.71 67.00 84.68 -73.80 13.65

Observed Results:
Grass is place on sculk.

Expected Results:
No grass is place on sculk.