will a pcie 3.0 work in a pcie 4.0 slot: Can I Use a PCIe 3.0 Card in a 2.0 Slot? - PC Guide 101. Can a PCIe 4.0 Device Work in a PCIe 3.0 Slot? (Answered). PCIe Slots: Everything You Need to Know | HP® Tech Takes.
A PCIe 4.0 NVMe SSD will work in a PCIe 3.0 M.2 motherboard slot at PCIe 3.0 speeds.
However, it's important to note that the graphics card will operate at Pcie 3.0 speeds in a
Pcie 4.0 slot, as it can only transfer data at the rate supported by the graphics card itself.
Likewise, a PCIe 3.0 SSD also can be inserted into a motherboard with PCIe 4.0
slot, and you will only get PCIe 3.0 performance.