God as a word/concept is ambiguous, it can mean something personal, unique and different to each individual. Some God views could be considered valid by Buddhism, though the typical one isn't.
Deconstructing the typical God belief:
These 4 qualities are often assigned to God by theistic belief system's:
(1) Omnipotence, no other being or god can match the 1 God's power because the 1 God is absolutely omnipotent and thus above and beyond all other beings and the world.
(2) The creator of all things that was before all things.
(3) Personhood or some form of individual conscious being that is distinct and disconnected from everything else or simultanesouly one with everything while still distinct as an individual.
(4) This being is eternal.
According to the Buddha belief in or holding any of the above 4 God views is not required (not even beneficial, in fact harmful) in order to lead the holy life, namely: Practicing the Eightfold Path; cultivating moral/ethical behavior; training the mind to be clear, calm and concentrated; achieving total freedom from harmful qualities and the permanent end of suffering.
The Buddha totally focused on teaching only that which is beneficial to the practice of the holy life and that which is true.
Holding the belief in such a God, will very likely for many people, lead to conflict between individuals, the development of harmful sectarian organizations and finally wars.
Ultimately holding the 4 false 'God views' is in too many ways far too dangerous (surely countless discussions could be devoted to deconstructing and invalidating these 4 false views) and is in no way required in order to practice the holy life and achieve the ultimate final fruit of the holy life (Nirvana).
Even if Nirvana equates to the heaven of theistic religions and there is a God that holds all the above 4 qualities, belief in a supreme being is still not necessary to practice the holy life and achieve Nirvana.
I cannot imagine a scenario where an arahant, a supremely perfected being who has eliminated all impurities/"sin" and achieved the highest evolutionary potential of mind, would approach the gates of heaven and find God saying "well that's all good but since you didn't "believe" in me you can't come in". That to me is projecting a corruption of human ego onto God.
Psychological Projection is a universal and harmful phenomena of humans. When there is a God belief all manner of imagination and ego traits are projected there on.
It is said the Buddha did not hold any beliefs/views. He was in total awareness of truth/reality, as it is, through his own direct experience/cognition. He looked and found there is no God that holds those 4 common theistic qualities. Seeing that there is no God like that, aiming to teach what is true and beneficial and seeing the dangers in those views, he taught accordingly.
Belief by my understanding means a view or concept that is held but where one does not have a direct experience, a direct insight of truth/reality. Only Belief's that are beneficial to cultivating the holy life should be held. For one who's vision of reality is purified and all harmful qualities permanently eradicated, belief has ended.
The unity and harmony of all things. A deep abiding peace and calm. Sublime love for all beings. Freedom from the disturbance of lust and anger. Unexplainable experiences that transcend time and space. Experiences so profound and deep that they change us for the better and show us a holy path. When people have these experiences they often say God in a many variety of ways. In these ways there is God in the Buddha Way. But no God that holds the 4 common theistic attributes.
There is no omnipotence and no being that is omnipotent.
There is no 1 being that is the creator of all that was before all. The universe has no beginning so no first creation. (If it can be said there is a being who is the creator, that being is all beings, we are all God and creation/destruction is a cycle with no beginning and no end.)
There is no being (nothing at all in fact) that stands independently outside of and disconnected from everything else. This is an 'atta'(self) misconception. (Some say there is neither oneness nor difference, others say there is both oneness and difference, but in any case that oneness/difference or neither oneness/difference is not omnipotence nor ultimate creator)
Impermanance is a fundamental characteristic of the universe. Projecting impermanence on a God being is like an extension of omnipotence. This is an 'annica'(impermanence) misconception.