One philosophical argument for existence of supernatural.

[Mystic]

Hahaha. Oh no no no. Stop generalizing

Bring evidence that opposes moral nihilism. And even if there was evidence that opposes it, at the end, most of humanity doesn't believe in morality due to that evidence, but based on faith.

The "how" is of prime importance: otherwise you're just making spurious claims about what is possible, and ignoring probability entirely.

In this case it's not. A person can simply say he knows value/praise to exist objectively without knowing how. He can say I don't know how, but I do know they exist. This is not a unreasonable answer. It's the same with morality. We don't have to explain how we know moral nihilism is false, to know it's false. The same is true of belief in free-will.