Causal determinism and non-materialist atheism

I'm (tentatively) conceding some ground in this post against CS Lewis. So no particular argument here; just for your end-of-year enjoyment.
If causality holds universally, then the universe is deterministic (_in principle_, and aside from quantum indeterminism).
Different versions of compatibilism attempt to reconcile causal determinism with free will to varying degrees. I'm not intending to go down that rabbit hole here——I'm wondering instead about rationality, reason, and materialism. Here's a one claimed problem (apologies if this is old ground for you):
"C.S. Lewis, in his work Miracles, builds an argument from the oddness of reason, claiming that a materialist-atheist view of reality is untenable. Imagine a purely materialist world: a world of only particles and matter, with no purpose or normativity——only causal relationships. In this world, reasoning becomes just a series of brain states caused by non-rational processes. According to Lewis, this means the rationality of thought processes is an illusion. If materialism is true, then there are no reasons, only causes. Thus, materialism undermines reason itself."
The algorithm read my mind and gave me an answer at Joe Folley's YouTube channel Unsolicited Advice (which I highly recommend). He describes himself as an agnostic/atheist, and offers this response:
"...Plantinga argues, there is no reason to think that survival and having access to capital-T metaphysical truth are necessarily connected..."
However (and I find this fairly reasonable):
"...For Fodor, sure, our ability to reason's overall job is to help us survive, but it does this through letting us know what the state of the world is—that is, what is true and what we can deduce from what we already know is true. At the very least, he suggests it needs to be shown how exactly a creature could have mostly or all false beliefs and yet still somehow be well-suited for survival. After all, beliefs are a big part of what guides behavior, and if we want to successfully interact with the world—that is, to achieve our aims of survival and reproduction—we had better have true beliefs about how the world will respond when we perform certain actions. Or, to use an example, we need to know where the tigers actually are, because if they are there, they can hurt us."
Interestingly, he then goes on to disagree that atheism implies materialism, and discusses the possibility of non-materialistic atheism with reference to Plato's forms and mathematical abstractions:
"In a recent video by the underrated YouTube channel Emerson Green, he points out that in modern popular discourse, we often use the terms atheism and materialism as if they are totally interchangeable. Lewis arguably falls into this trap as well when he suggests that if his argument from reason succeeds, then this is good evidence for God’s existence. In his video, Green largely talks about the examples of non-materialist atheism from the philosophy of mind, but I want to expand upon this point because there is a whole world of non-materialist atheism to explore. And a lot of it is far less ridiculous than you might first think."
"The Hidden Problem with EVERY Atheist Argument"
https://youtu.be/Q1jQscSNtNU?feature=shared
(Don't be put off by the title)