How to determine from command line if NVMe slot is gen 3 or gen 4?

On 12th gen motherboard, what happens if you plug a Gen 3 SSD into a Gen 4 Slot and

PCIe® Gen 3 NVMe Type 1620 HSBGA SSD; SecurStor-enabled managed 2 modules designed for a SATA interface will perform according to the

m2 pcie 40 in 30 slot socket 3, Key M, Processor is AMD Ryzen Is a half-length PCI Express x8 Gen 3 card compatible with a PCIe x4 Gen3 slot?

m2 vs nvme slot slot) In fact I've even successfully used a x4 adapter advertised as PCIe to run a Gen 4 drive at full speed in a PCIe slot: WD