Seems that the Notebook uses not a standard 2280 m.2 SSD but instead a much smaller one (maybe 2230). I just wanted to install a Samsung 980 Pro on my exemplar but aborted the operation.
The SSD is under the Metal Frame in the Middle above the Battery.
Btw.: Disassembly is pretty easy: Just remove 4 screws and use a suction cup on the front corner on the bottom (not on back side at hinge area which seems to be much stronger).