I bought the new Samsung 980 Pro 1TB (PCIe 4.0) and put in the Lenovo Yoga Slim 7 (PCIe 3.0), I saw only ~10% decrease in raw performance : r/AMDLaptops
Samsung 980 Pro Ssd M2 Nvme 1tb 2tb 500g Pcie Gen 4.0x4 M.2 2280 Internal Solid State Hard Drive For Ps5 Pc Laptop Playstation 5 - Solid State Drives - AliExpress
Samsung 980 Pro NVMe SSDs with blazing fast PCIe 4.0 speed launched - Channel Post MEA
Samsung 980 PRO PCIe 4.0 SSD | Samsung Semiconductor Global