Install a guest Win10 in VirtualBox in Ubuntu 20.04 from ISO

Question

I have followed the instructions here (and posted many places else in various forms, 1) to boot from an iso image of Win10 under VBox in Ubuntu 20.04.

I get Fatal: Could not read from the boot medium! System halted

What am I missing?

Notes:

1. I actually posted first Install a guest Win10 in VirtualBox in Ubuntu 20.04 from USB. Since the difference between booting from a USB installer or an .iso image installer may be significant, I later changed the title of the other question to specifically address the USB case, and this one to address the .iso image case.

2. I managed to import the ova image obtained here, MSEdge - Win10.ova, but it is not the same.