Hello,
please explain how to configure PCIE0 (boot nvme) to 1 lane?
No configuration needed. Just plug in your SSDs, and the system will figure out if it is 1, 2, or 4 lanes width. You can’t use the other lanes for a different device, though. For custom boards you always should route all 4 lanes to an M.2 type M regardless of the module you are going to plug in.
This is the question. The custom board have route only 1 line. Other lines don’t used at all.
The answer is still same. You don’t need to change software configuration.
If there is only one lane in use, then software driver will make it into x1.