On checking if a rabbit can spawn, it checks for if the block below is grass, sand, or if it is a snow (a snow layer). From what I can tell, this should be snow block.

Snow layers will fail to have successful spawn, unless they have layer=8 as those are normally spawnable. Rabbits will therefore spawn on them. However, these do not generate naturally, as opposed to grass and sand.

Relates to: https://www.minecraft.net/en-us/article/minecraft-1-14-2-pre-release-1 "Fixed so parrots can spawn on grass blocks and not only on grass"

In the screenshot, the left is snow block, the right is 8 snow layers.