The argument is one of Philosophy, epistemology- what can be ‘known’ and how? Of course like all discourse it depends on what the basic words mean- what does it mean to ‘know’ something.
All sentient beings by definitions have beliefs and belief systems. You cannot contradict the possession of beliefs- they are there because they are there, not for any other reason. They are an element of being sentient.
Knowledge is a different matter and is defined differently by different groups!
To ‘know’ something is to have a belief that is justified by some external support other than being a mere fleeting sensation in the brain of a sentient being. It is a social construct- agreed by the group of people sharing that method of validation of knowledge.
If a group of people come together and share their beliefs in a Theistic God, claiming direct internal experiences of interaction with that God, then within that system, ‘God’ exists. This is not disimmilar to Gilbert Ryles argument about the existence of Oxford University (which has many colleges, an administration structure, lecturers, professors, students and bulldogs) but has no campus- nothing that can be pointed to and said about ‘Here is the University’. It includes much of the city of Oxford and many of the lands in South East Britain (it being siad that one could walk from Oxford to Cambridge on University land!) It is convenient to admit that such an inchoate structure is in fact one object- a University. Everyone (well almost everyone) goes along with this.
The Scientific Method has a different approach to ‘Knowledge’, insisting that to be Knowledge, it must be testable, Falsifiable and agreed by a sufficient group of skilled scientists to be Knowledge.
The difference is that mere agreement is not necessary, that there must be some foundation in the world around us.
Science has advanced by gradually stripping away beliefs that were seen as true and unknowable (causation by gods, elves and others, the Aether, Phlogiston, Life spirits, human souls, free will, and so on) by explanations not dependent of belief supported only by agreement.
Because Science (and the Technology following it) has been the one system that has created the modern world, it is now seen as the default for both Epistemology (what we know) and Ontology (what there is.)
God ‘exists’ and is ‘known’ in a different manner to the existence and knowledge provided by Science.
Science is quite happy for the existence of God to be investigated by the scientific method and proved to exist, but this has never been practically achieved, and many philosophers would insist that the program to prove the existence of God misunderstands the concepts involved.