Minecraft wiki entry for Mycelium, associated text: Mushrooms and fungus can remain on mycelium blocks in any light level, unlike the situation on other blocks, where mushrooms are broken (dropping as items) during block updates in high light.
Huge mushrooms can grow on mycelium, just as they can grow on dirt, grass, or podzol.
Mycelium cannot be tilled with a hoe to make farmland.[1]
However, it can first be converted to dirt path using a shovel, then tilled with a hoe to create farmland.
In Bedrock Edition, pumpkins and melons do not grow on it.