A manga where the MC is the strongest mage and he already defeated the demon lord in his world just to test out his power. He was then summoned to another world that summoned the strongest people from different worlds to fight their demon lord. He ended up being too strong that the scanner couldn't pick up his power so they thought he was super weak(unless I'm remembering that last part wrong)

Edit: I found it, it's called I Was Exiled From the Heroes' Party So I Tried Raising the Demon Lord to Be Unbelievably Strong