[Laforet]

Scenario C is more likely the culprit. I have seen multiple examples of prebuilt PCs and laptops defaulting to software RAID mode for reasons unknown, and they did not always have a toggle just like in OP’s case.

The only time I have come across scenario B was with a VAIO laptop from around 2011. The machine was advertised to come with “fastest SSD on the market” which turned out to be four (!) off the shelf eMMC modules in RAID 0 through a hardware controller. As janky as it sounds, OS compatibility was never an issue because the controller was a fairly common model with well established driver support rather than some bespoke mystery.