'One God' is an assertion, for which no proof has ever been given for either for one God or many..
God is like a blank drawing sheet, you can draw any image on it. One can draw one figure or one can draw a multitude.
The philosophy of science limits science to just data that comes into the brain via the sensory systems. Science takes an extroverted approach to reality; interacts with the environment. Science, by its own philosophy, can not fully deal with internally generated data from the brain. Dreams, from example, need to viewed from the inside and cannot yet be viewed from the outside via tools that extend the five senses and conform to the philosophy of science.
God appears to be connected to that internal zone, where the philosophy of science does not allow science to fully go. Science, like psychology, which does attempt to deal with internal things, like dreams, is called soft science, since it has to take liberties with the stricter rules of its extroverted philosophy. The psychologist may ask their patient to give details for what they feel or think and will have to take their word for it, without external verification. The may have to rely on on experience and trends. This is where softness appears.
The fact remains that science has not been able to find God using its extroverted philosophy. Science appears to have shown that God is not outside us, in form that we can perceive with our five senses. Yet, even given the chance to deny God, via the logic supplied by atheism and the philosophy of science, billions of people still appears to get internal verifications that make them what to believe in God.
These internal verifications has been going on since the dawn of civilization and still occur in modern times.There is something there. This is why dreams and visions are an important part of religions; prophesies. Science would need to upgrade its philosophy, to include internal verification, or come to terms with the fact that its current philosophy is not designed; too limited, to deal with internal consciousness phenomena of the human brain. A microscope cannot see dream details. This does not mean they do not exist. It means the wrong tool and wrong approach is being used. It will guarantee failure, which is then called success, based on unconscious internal reality overlay.
If you look at any innovation, they all begins in the mind of a creative person. If you were to ask science to verify this new idea, in advance, they are not suited to do this since it is only a seed that lack form. They will instead deny it, until the day comes with they have something tangible to investigation, within the limits of its philosophy. Science cannot deal the internal reality driven budding of innovation. They have to wait until late in the process so they can use an external approach.
For example, the iPhone began as an idea in the imagination before it became part of reality, so science could investigate. God works the same. God is part of continuing creation. The vision of Jesus of a religion, preached to the entire world, was easy to deny, via all the extroverted philosophies, until it became manifest. The charisma of faith is baed on experience from the inside. This is the same source that has advanced all areas of science; internal processes and extrapolations outside one's own time.