m.2 slot pcie - Suspended Domain
Similar to the PCIe expansion slots of your motherboard, the number of PCIe M.2 slots it will offer also depends on the number of PCIe lanes your motherboard supports.
What are Small PCIe x1 Slots Used For? - CGDirector
If you have a desktop motherboard with 3 PCIe x16 slots and your graphics card is inserted into the second or the third x16 slot, it will mainly use 8 or 4 lanes, respectively.