Rock 4B+ PCIe on M2

I bought this cable to insert a PCIe 2.0 network card as shown in the photo.
I wanted to know if the M2 slot is dedicated only to SSDs, or through this adapter, even if I don’t have the drivers, should I see the device with “lspci” ?
For now it doesn’t work I’m trying to figure out if it’s the cable, or some configuration in the hw_intfc file, or it can’t be used for uses other than SSD disks.
I need to mate a PCIe card to an SBC board.

Many thanks to anyone who can clarify the use of this port.

Can anyone tell me anything?
Have you tried installing a PCIe card?
Is the M.2 M bus compatible with PCIe 2.0 at the hardware level?