PCIe 4.0 M.2 on AM4 board?

Correct that both the chipset and the CPU needs to support PCie 4 - so thats B550 as an example if you want AM4 - and Zen 3 (5xxx) CPUs mostly do support PCIe 4 0 but not the 5600g. The number of M.2 slots and other slots a m/b actually has, and how many actual lanes can be used simultaneously also needs checking. But if the application really needs multiple PCIe4 then maybe youre looking at AM5 / DDR5 level with discrete GPU rather than 5600g,

I am pretty sure B550 only includes one PCI 4.0 slot and if you wanted one more you'd be looking at the X570 motherboard lineup.

No you don't need the components to all be PCI-E 4.0 for it to work. For immediate example you can put a gen3 NVME in a gen4 slot, but it'll be bottlenecked and it will only perform to gen3 speeds.

AM4 Ryzen CPUs that have integrated graphics (like the 5600g) will disable gen4 on the board, it's the biggest let down for the integrated graphics part, but this can be easily fixed by finding a used GT710 on eBay for £15-25

Majority of AM5 Processors support integrated graphics, excluding the ones that have an "F" after the number set in the list.

Hope this answers all your questions

so what would be a reasonable expectation of mb/s throughput of a fast gen4 nvme drive running with a 7600g on a b550 board assuming max lanes active.

is a gt710 as fast as 7600g zen3? i have a radeon hd 7800 2gb i could use. any downside to that in 2d desktop work?

only want one m.2 slot.

thanks (edited)

Are you actually using the sequential transfer speeds in any significant way? Most workloads are going to be limited by drive performance rather than the interface.

not really. just wanted to get the best bang for my buck.

Just get a pcie card to add m.2 drives. Something like this...

ebay.co.uk/itm…BwE