PCIe x16 Link to GPU detected with "limited by 16.0 GT/s PCIe x4"

I'm trying to establish a stable connection to my RTX4090 by using 2 PCIE MCIO x8 connections. The board is an ASUS K14PA-U12. The Device adapter is from cpayne "MCIO PCIe gen5 Device Adapter 2* 8i to x16".During startup dmesg shows the following for the NVIDIA card:

[    1.258785] pci 0000:c3:00.0: 63.012 Gb/s available PCIe bandwidth, limited by 16.0 GT/s PCIe x4 link at 0000:c0:03.1 (capable of 252.048 Gb/s with 16.0 GT/s PCIe x16 link)

Device 0000:c0:03.1 is a PCI bridge capable of x4 only:

>lspci -v -s  0000:c0:03.1c0:03.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 14a5 (rev 01) (prog-if 00 [Normal decode])>lspci -vv -s  0000:c0:03.1 | grep LnkCap LnkCap: Port #0, Speed 32GT/s, Width x4, ASPM L1, Exit Latency L1 <64us

OS is Ubuntu 22.04. Why is the system detecting the PCIe device with only 4 lanes?Any BIOS setting necessary?

Thank you in advance