Never-mind! It seems to be a problem with the Focal (4.4.y) image. I downloaded the Focal (5.10.y) image and it's worked as described. Which also means that the XPG SX6000 Lite 128GB PCIe 3D NAND PCIe Gen3x4 M.2 2280 NVMe (ASX6000LNP-128GT-C) works well with this setup. Its a cheap and cheerful NVME purchased from Amazon.
Now I just need to get nfs server working to share data between my Macs and other servers (ubuntu and Raspbian). I've found a few hundred tutorials and they are all just a little different and so far none have worked. :-/
Thanks for the great work on this!