Inspiron 17-7779 does not support PCIe SSD's, only SATA SSD's

Please answer this question for me. Why in the world is the open M.2 slot in the 17-7779 specifically designed to take an ‘M’ keyed 2280 SSD when it doesn’t support PCIe and NVMe which are the only ‘M’ keyed 2280 SSD’s on the market? From what I can see, an M.2 SATA SSD the dual ‘B’ & ‘M’ edge connectors will work, simply because it is SATA based. What is driving me insane is the fact that the physical M.2 slot in the 17-7779 is specifically designed for ‘M’ keyed devices, not ‘B’ keyed devices. It makes sense that a dual keyed device will work, but only PCIe devices utilize ‘M’ keying alone, but the 17-7779 (even though it seems to be physically designed to) doesn’t support PCIe, why?

Some background: after much frustration, research, and testing, I have conclusively determined (confirmed by Dell Tech Support) that the 17-7779 does NOT support PCIe SSD's in its open M.2 SSD slot. While this is technically (no pun intended) described in the specifications manual, it is not very clear and has left a lot of 17-7779 owners with useless PCIe SSD’s in their hands. In the specifications manual, it lists SATA as the interface but, very ambiguously lists only the generic term M.2 as an option for SSD. With most forums saying PCIe and NVMe are backwards compatible, many people, like myself, have been left up the creek without a paddle.

From what I can tell, the specifications manual is definitely NOT enough information for a user to make an informed decision on purchasing an SSD for their 17-7779.

All of this leads me back to the design of the M.2 slot in the 17-7779. It seems to be physically designed to support PCIe lanes (in the form of ‘M’ keying), yet it doesn’t logically support it and the motherboard is unable to communicate via NVMe, even though NVMe is supposed to be backwards compatible. This is nuts! Someone please help answer this question, and also get Dell to create a workaround for this, even if it means replacing the entire motherboard.

If I am being confusing with all of this, perhaps this will help: find me an M.2 2280 SSD that uses the SATA interface and has the ‘M’ edge connector ONLY. Not ‘B’ keyed or dual ‘B’ & ‘M’ keyed, only ‘M’ key. Remember, M.2 2280 SATA with the ‘M’ edge connector only. I feel like this search alone gives perspective on my question. Thanks for any help you all can provide!