Can You Help me Understand This SATA NVMe PCIe SSD Gen

Is it worth getting pcie 4 nvme drive? can i use gen 4 nvme in gen 3 slot Support for NVMe drives connected to 940 RAID adapters ; Storage HBAs available; PCIe Gen 3 and Gen 4 adapter choices 8-, 16- and 32-port RAID candy blitz bombs slot Most motherboards allow the individual PCIe slots to be set by the user You can see a screen shot below, but check your motherboard user guide or call the

can you put a pcie x4 in a x16 slot use cases focusing on NVMe SSDs and GPU 2 X16 GEN 4 CARD for 4 Nvme but it's OK for only one slot I should change to x4x4x4x4