Ethics exist independently of any deities even if they did exist.

If ethics didn’t exist separately, and God is actually the source of good, then we would have a lot of logical paradoxes to solve.

For instance, let’s assume God is who defines goodness and educates us on it, and goodness does not exist without God.

Thus, we recognize we don’t have inherent ability to define what’s good or bad. But that also means we can’t prove God is good, because we already recognized only God can define what’s good.

I might have butchered the logical fallacy a bit, logic is hard, but I remember it roughly being stated this way.