I think Descartes was a deist (I am). I gather from his writings that he did arrive to conclusion of existence of the Higher Being. Originally an atheist, I did too - after studying physics, engineering, anatomy, biology. I find all religions being dogmatic and not able to explain existence of God/Higher Being - more like a collection of fairy tales and instructions/directives.
The key principle that he derived is 'Cognito, ergo sum' (I think, therefore I am), and it changed the course of Philosophy forever. This principle permeates through all his writings.
From his 'Discourse on the Method':
Accordingly, seeing that our senses sometimes deceive us, I was willing to suppose that there existed nothing really such as they presented to us; And because some men err in reasoning, and fall into Paralogisms, even on the simplest matters of Geometry, I, convinced that I was as open to error as any other, rejected as false all the reasonings I had hitherto taken for Demonstrations; And finally, when I considered that the very same thoughts (presentations) which we experience when awake may also be experienced when we are asleep, while there is at that time not one of them true, I supposed that all the objects (presentations) that had ever entered into my mind when awake, had in them no more truth than the illusions of my dreams. But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be something; And as I observed that this truth, I think, therefore I am,[c] was so certain and of such evidence that no ground of doubt, however extravagant, could be alleged by the Sceptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the philosophy of which I was in search.[f][g]
https://en.wikipedia.org/wiki/Cogito,_ergo_sum
The movie 'Matrix' in based on this. We experience and make decisions in this world empirically based on our 5 senses, and how do we know that they don't lie to us? Humans in pods had all their sensory signals fed with fake data.