I thought others might benefit from my experience. The problem was solved but it was rather strange.
I tried to install Windows from an ISO image created by the Windows media creation tool. It didn't work. Eventually I figured out it was not seeing enough free space for temporary files, but my C: drive has more than 500GB free.
I went into DISKPART and after much rooting around discovered that the GUI ID for my EFI System partition was wrong. I'm guessing this happened when I expanded it to 500MB from 100MB as per HiltonOishi's suggestion in https://answers.microsoft.com/en-us/windows/forum/all/failed-install-attempt-error-code-0x800f0922/c5eb31d7-f04f-4ff8-9d6f-f39e4f03944b.
I set the EFI partition's GUID to c12a7328-f81f-11d2-ba4b-00a0c93ec93b as it should be and retried the Windows installation from ISO. This time it seemed it would continue, so I interrupted it and ran the update I had been trying to install, and it installed without a problem.