The key of that quote is here: "Those lanes are split into x16 or
x8 for GPUs, or x4/x4 for storage slots". The "x8" split I talk about gets further divided for whatever purpose they want to give it; my take is they're using that on this gen Z690 for the plethora of NVMe drives and sATA ones, unless they're using only the DMI4 link, which implies they'll need to cut something else from transfering (being used) and make just 1 (or 2, tops) NVMe slots full speed as the CPU only exposes 1 x4 PCIe4 for it (them).
As I said, it's up to the motherboard maker how they "divide and conquer". AMD motherboards also have this kind of fine print with more than 1 NVMe drive in it. This chipset can, maybe, get away with 2 NVMe drives from the CPU at full speed without tapping into the PCIe5, but I seriously doubt motherboard makers will include the muxers required to do that, so maybe they're just abusing the DMI link and have only 1 NVMe linked to the CPU.
Here's a good breakdown of the Z690 features and a diagram:
https://www.guru3d.com/news-story/i...cie-5-x16ddr4-or-ddr5-memoryand-dmi-4-x8.html
Regards.