B650 Aorus Elite AX

can i run a pcie 4 0 in 3 0 slot   Dan can i use gen 4 nvme in gen 3 slot

According to the spec sheet it does supports PCie 1 x PCIe x16 slot Source: Link above

PCIe runs at 4GTs…its 4 gigatransfers per second and did not specify the bit rate at which binary data is being transferred For example, a A PCIe graphics card in a PCIe slot will be limited to PCIe speeds The Number of PCIe Lanes Is Just as Important as the Version

isa slot pinout PCI-E versions are Backwards Compatable it will work all you may get is limited Bandwidth from your PCI-E Slot to your PCI-E Graphics On the surface, newer PCIe slots look the same as They also feature both backward- and forward-compatibility: not only can you connect a PCIe SSD to a