Dragos Manea :
Usually add-ons cards are using motehrboard pcie lanes, wi-fi card or nvme and so on are using motherboard lanes by default, and GPUs are using cpu lanes by default and i dont think you can change that because i tried to set my videocard on 8x but i never got the options to switch my other pcie devices to cpu lanes. Long story short any peripheral or storage card is using motherbaord lanes, cpu lanes are used only by important hardware like videocards, or videoprocessing cards or anything that needs a fast data transfer and low latency (storage isnt one of it).
It depends on the slot you use. The motherboard's manual will tell you. In his board's case there are 4 GPU slots and all 4 connect to the CPU, so if you put ANY card in those slots they will use lanes connected to the CPU. the slots are hard wired, there is no way for it to decide what lanes to use depending on device.
Its most likely his M.2 slot uses the chipset's PCIe lanes, not the CPU. Also he should just put his PCIe SSD into one of the non GPU slots, because it will run at x4 anyway and he doesn't need to worry about this issue, theres no difference in performance of the drives.