I’m admittedly not the most informed geek on 40K lore, but I do follow it a fair amount. I thought the setting always left it ambiguous as to whether all the mysticism around technology was truly needed or mere superstition. Demons are obviously real, but they’re a product of psychic activity and the extra-dimensional warp. Demons are never directly invoked by interacting with technology. Rather, the consequences would be angering the machine spirits and your Thunderhawk’s engines shutting down and crashing out of the sky.
As far as I understand it, it’s open whether mysticism (e.g., a hypothetical Litany of Boot-Up that should be chanted before booting up your laptop) is:
completely unnecessary superstition. To the extent “machine spirits” exist, it is semi-sentient AI that isn’t recognized as such.
absolutely necessary. Angering the machine spirits can lead to all kinds of problems from a failure to boot to the machine blowing up in your face.
A cynical power-play known only to the highest orders of the Priests of Mars. Everyone else fervently believes it’s 2), but it is really 1).
My recollection, for example, is that in the Horus Heresy books (of which I admittedly have only read like 2-3 of the 100s that they’ve seemed to have written), there isn’t any of the mysticism surrounding technology, and yet everything still works.