I made the USB flash drive, and I also disabled secure boot.
I can see the EFI partition with option key at startup. I get the Windows icon for about 15 seconds, then a blank screen, and the 16" eventually brings up the choose a startup disk dialog box.
So, Im not even able to install Windows fresh with Boot Camp Assistant, nor via the flash drive.
I called Apple Support yesterday, and after 20 minutes with Tier 1 Support, I was escalated to Tier 2. He said the problem with not being able to contact the Software Update server at the start of the Boot Camp installation process is a -Microsoft- problem, not an Apple problem.
When I told him that I had a late 2017 Macbook Pro 15" whose Boot Camp application can connect to the Software Update server, he said it may be that Microsoft may not have “profiles” for the 16" machine yet.
However, an hour of Googling indicates this problem has cropped up from time to time before, and some posts give web addresses for the server swcdn.apple.com, which I was able to ping and traceroute to. Very slowly.
I have a week to return the new MBP to Apple…I have some essential Windows applications I need to run, so let me know if you (Two Canoes) get Windows running at all, and then if you can restore a WinClone backup successfully. If you can’t I’ll return the new 16".