Now there's some fresh information about the PCI Express support of Alder Lake-P, which is a mobile series. Tom's Hardware writes new leaks indicate Alder Lake-P will have a flexible PCI Express layout with PCI Express 5.0 and PCI Express 4.0 lanes:
Alder Lake-P appears to provide a flexible PCIe layout. The processor reportedly offers one PCIe 5.0 x8 lane or two PCIe 4.0 x4 lanes. It would appear that neither interface supports bifurcation, meaning you can't split up the PCIe 5.0 lane or get the PCIe 4.0 lanes to operate at x8. Nonetheless, both are backward compatible with previous-gen devices.It's not sure if Alder Lake-S will have the same configuration. One PCI Express 5.0 x8 lane offers 32GB/s of bandwidth, which is the equivalent of PCI Express 4.0 x16.