This might work as intended but if fortune on an axe doesn't work for mushroom black what is a fortune exe good for?
Environment
When mining mushroom blocks with a fortune axe it rarely drops any, I checked the loot table for the mushroom block and it doesn't have a fortune function.
This ticket concerns a feature request or parity issue; as this is a bug tracker, this ticket will be resolved as invalid. Alternatively, please visit Minecraft Suggestions on Reddit or the official feedback website.