Moving boot SSD from Gen3 slot to Gen 4 expansion card?

Should you buy a PCIe or SSD? can i put a gen 4 m 2 in a gen 3 slot ➤ High-speed NVMe PCIe Gen3 x4 Interface:combine the next-gen PCIe Gen 3x4 NVMe interface with the latest V-NAND technology and a newly enhanced Phoenix candy jar clusters slot Solved: Does installing gen4 NVMe SSD on PCIe 3 slot affect the speed? or should i buy 3 gen3 NVMe ssd? Please give me some advice

can i use a pcie 40 gpu in a 30 slot 2 x16 Gen 4 Card is compatible with the Intel® X299, Z390, Z370 and future platforms' RAID-on-CPU function, and supports PCIe NVMe RAID on the AMD TRX40 and