My initial excitement about retimer card from Supermicro turned out to be premature. I could not get all 8 drives to be seen by the system. Two out of 8 disks would go missing. I had to go with a much more cost effective solution instead by ordering PCIe to SFF-8654 Adapter PCIe 4.0 x16 to SFF-8654 (2x) 8i for U.2 NVMe SSD:
(No included SFF-8654 to SFF-8639 cable). PCIe to 8654 Adapter. Interface 1-port 4i SFF-8654 2-port 4i SFF-8654 2-port 8i SFF-8654. PCIe PCIe 4.0 X4 PCIe 4.0 X8 PCIe 4.0 X16. Not support SAS or SATA SSD.
www.ebay.com
Now all drives are present and I can continue populating bays with more drives once I get my hands on them.
Moral to this story - simple bifurcation works without any fancy hardware.