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 PCIe 4.0 NVMe SSD Review - StorageReview.com
Samsung 980 PRO Review: A Powerful PCIe 4.0 NVMe | Dong Knows Tech