Laptop M.2 connector confusion (Qualcomm Atheros M.2 connector)

Question

I was wondering if my laptop could support a M.2 PCIe SSD. My laptop is an Acer Spin 3 315-51-757c specs on CNET. Unfortunately, Acer doesn't seem to provide a service manual, but rather only this user manual, so I can't seem to find any information online.

Before today, I had no knowledge of the M.2 interface. My understanding now is that M.2 is an interface that can support either PCIe (fast) or SATA (slower) SSDs. The CNET specs do mention that the WiFi/Bluetooth module Qualcomm Atheros QCA9377 uses a M.2 interface, but mentions nothing about another one for storage; however, other Spin 3 models do seem to have a M.2 SSD (e.g., this), so I thought this laptop might as well.

I'm confused because I do see two M.2-like interfaces, but they look different. Here is the laptop and the two M.2 interfaces (one is just right of the fan, and the other is at the bottom-left with the WiFi card plugged into it.)

Here's the unused M.2 up close. It seems very clearly to be an M-edge M.2, and I have no problems with it. It would fit an 80mm SSD perfectly, so I'm going to try to install a SSD in it.

Here's the M.2 with the WiFi module in it. This is what I'm confused about. It's the same width as the other (22mm), but the notch is at a different place (and not a B-type M.2 connector). I thought it might be mPCIe, but it seems to be a little wider than M.2 (30mm). Again, the CNET calls this an M.2, but what is it?

Secondly, I'm also confused about the shape of the WiFi module. It has two notches -- the left one looks as though it should fit into a B-type M.2, and the other notch fits into the connector it currently lives in. Interestingly, it also fits snugly into the M.2 connector:

(I tried to boot with it in like this, but the power LED flashed and it wouldn't boot for another minute, so I guess that's not supposed to be like that.)

Another confusing thing is that when I run HWiNFO, it lists a PCIe 3.0 x1 (with the WiFi module), a PCIe 3.0 x2 (with a RealTek Card Reader -- I'm assuming this is the SD card slot?), but nothing else. The same is true on Linux -- the output of lspci is this (the last two lines are relevant). These tools don't seem to be helpful with telling what interface the PCIe devices use, and don't seem to be picking up on the unused M.2.

00:00.0 Host bridge: Intel Corporation Xeon E3-1200 v6/7th Gen Core Processor Host Bridge/DRAM Registers (rev 02)
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)
00:14.0 USB controller: Intel Corporation Sunrise Point-LP USB 3.0 xHCI Controller (rev 21)
00:14.2 Signal processing controller: Intel Corporation Sunrise Point-LP Thermal subsystem (rev 21)
00:15.0 Signal processing controller: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #0 (rev 21)
00:15.1 Signal processing controller: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #1 (rev 21)
00:16.0 Communication controller: Intel Corporation Sunrise Point-LP CSME HECI #1 (rev 21)
00:17.0 SATA controller: Intel Corporation Sunrise Point-LP SATA Controller [AHCI mode] (rev 21)
00:1c.0 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #4 (rev f1)
00:1d.0 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #9 (rev f1)
00:1f.0 ISA bridge: Intel Corporation Sunrise Point-LP LPC Controller (rev 21)
00:1f.2 Memory controller: Intel Corporation Sunrise Point-LP PMC (rev 21)
00:1f.3 Audio device: Intel Corporation Sunrise Point-LP HD Audio (rev 21)
00:1f.4 SMBus: Intel Corporation Sunrise Point-LP SMBus (rev 21)
01:00.0 Network controller: Qualcomm Atheros QCA9377 802.11ac Wireless Network Adapter (rev 31)
02:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS5229 PCI Express Card Reader (rev 01)

Sorry for the slew of questions, but it's a bit confusing to me. Namely:

• Is the WiFi module connector some type of M.2? And is the empty slot an M.2?
• If the empty slot is M.2, how can I tell if it's PCIe or SATA if there is no visual difference, Acer manuals are proprietary, and software tools like HWiNFO and lspci don't list hardware interface types or unused interfaces? (i.e., can I use this for a NVMe SSD?)