can i use pcie 3.0 ssd in 4.0 slot
Can I Use a PCIe 3.0 Card in a 2.0 Slot? - PC Guide 101
A PCIe 4.0 NVMe SSD will work in a PCIe 3.0 M.2 motherboard slot at PCIe 3.0 speeds.
Can I Use a PCIe 3.0 Card in a 2.0 Slot? - PC Guide 101
Slot Type Size (Pins) Common Use Mini PCI 100 or 124 Wireless cards Mini PCIe 52 SSD storage, wireless cards. ... Yes, PCIe is backward compatible, so you can use a PCIe 3.0 card in a PCIe 4.0 slot without issues.
PCIe 3.0 GPU in a PCIe 4.0 Slot - Graphics Cards
With most new expansion cards coordinating with v3.0, it is common to ask: can I use a PCIe 3.0 card in a 2.0 slot?