Nope, I'll try to find the source, but it's a very custom thing since the controller is actually on the chip, so the thing you connect via M.2-ish is just the storage module. Therefore no non-Apple specific SSD will work on it, even if you can physically connect it because the connector is the same.

It has a different pinout in my experience. The exact spec changes between models, I think one or two models of macbook have a standard M2, some (most?) have what looks like an M2 but has extra pins when not actually soldered on.

My experience is only around trying to help a friend get the data off a fried board in a macbook, the desktops might be more standard.

I don't believe so.

I don't think the "U" notch and pins are the same.

But happy to be wrong :)

Yup. Looks like a 2230.

Edit: not a 2230. Different pins.