I made a little PCB which splits the x4 Lanes into 2x2:
I haven’t tested it yet. I ordered the wrong thickness (should be .8mm, is 1.0mm) and i still need to find out how to modify the PCI-E configuration in Linux. I’m still not sure what to do with the signals wake, clkreq and perst because they only exist once on the Radax M.2 port. The pins on the RK3588 intended for this signals for the second PCE-E port are already used otherwise
In the end it should look something like this:
It’s intended for a NAS with a PCI-E to SATA adapter and an NVME SSD