So we can't prove the existence of anything that is not physical, let alone the existence of a non-physical God.
Why believe in the existence of anything that is not physical?
To claim something is spiritual (non-physical) you are saying there is no way to verify that it exists.
I can believe there is a non-physical million dollars in gold in my closet.
While maybe I can convince someone to buy my non-physical gold, they ain't going to be happy when I tell them there is no way to prove the gold they just bought exists. They are just going to have to trust me on that.
Yet folks continue to sell us a belief in the non-physical.