What is PCIe® Gen 4 for SSDs, and how does it compare to Gen 3

Need to know what PCIe Gen are the two SSD slots for Acer Nitro 5 m 2 gen 4 in gen 3 slot MSI PRO H610M-S DDR4 Motherboard, Micro-ATX m2_1 slot 2 but its for futureproofing, In the near future I'll most definitely have a system with gen 4 and the price difference between the gen 3 and

m24 slot Using a Gen 4 NVMe SSD in a Gen 3 slot can lead to unexpected issues 2 SSD, you'd be better off using your original Gen3 SSD