Only for the few (<8 lanes) provide by chipsets older than 5xx series - the main quantity of PCI-E lanes are 3.0/4.0 provided by the CPU
https://en.wikipedia.org/wiki/List_of_AMD_chipsets#AM4_chipsets
In most cases none of that is connected to m.2 etc though right, where throughput is required it's all gen 3 at a minimum? The chipset is for things like sata, additional x1 & x4 lanes etc where the throughput won't saturate the lanes anyway or am I missing something here? Just seems a super odd selection to me if you are focused more on IO.