I believe they have a special kind of SSD, where the controller is locked into the motherboard. This is serial locked in some form.

(Correct me if I’m wrong, but this is how I understand it)

My understanding is that the controller is integrated into the SoC.

You can actually replace the storage on Apple desktops but it’s a bit of a pain and isn’t as cheap as m.2 2280 drives.

I don’t really know why Apple does this when their solution doesn’t seem to offer an obvious advantage. They aren’t faster than existing solutions or anything like that.