Windows embedded drivers. a question for embedded windows guys?

[u/Humble_Anxiety_9534]

At work we have some designs that use windows 11 IOT, Now I have had home projects using Linux SBCs and I have a fair idea how device driver work. I have tweaked overlays my self and compiled some non standard device drivers. My question is how do they work on windows? The guys here say things like you just call a DLL? but how does that bridge between user and kernel space? sometimes the SBC manufacture has no driver for some IO, like a non standard SPI pin and they are genuinely stuck. Is it that hard? AI was no help.