Mundane potion is a very useless potion. You can not use it to brew other potions and it has no effect when thrown.
Mundane Potion using brewing stand
Now you can make Mundane potion using a brewing stand. Go towards the brewing stand and put Redstone and a water bottle on fire to get mundane potion in a few seconds. Add this potion into your “ready to use” stock.
You can see Mundane Potion in the image below. Mundane potion is a useless potion, it can not be used to brew other potions.