That’s not what agnostic means. Agnostics believe “there is no way to know”, so you can have Agnostic Theists (we can’t know for sure, but I believe God exists) as well as Agnostic Atheists (we can’t know for sure, but I don’t believe God exists).
The opposite is gnosticism, and you can similarly have Gnostic Theists (God exists and I can prove it) and Gnostic Atheists (God doesn’t exist, and I can prove it).