Can A Supervolcano Eruption Really Wipe Humanity Off?

Yes.

.. but slowly, not by the explosion.

But the biggest killer would be the poisonous gases that will quickly spread across vast areas making air unbreathable for people and most would die due to suffocation. The ground would get covered by a 10cm layer of volcanic ash which would kill plants and trees leading to agricultural devastation.

Imagine that, but the full world.