Feature update to Windows 10, version 20H2 not downloading.  

A Windows 10 iso can be created on any working computer.
Downloads and or upgrades / updates can be performed overnight.

Paul Black said:

As it is a Mounted ISO, you should have just run the setup.exe.

That's what I did. I mounted the ISO and double-clicked setup.exe. The first question it asked me upon opening it was whether I wanted to check for updates, and I selected the option to do so. For some reason, it's taking a long time to check for updates. It's up to 33% now.

If I were you, I would not have selected the option to check for updates so as not to complicate matters.

Matthew Wai said:

If I were you, I would not have selected the option to check for updates so as not to complicate matters.

It finally finished. It's now on the "Ready to Install" screen. Should I proceed?

Yes, proceed.

hbenthow said:

I put a lot of work into customizing Windows and installing programs. I don't want to lose that.

Customization and installation can be done by scripts automatically.

Ghot said:

Well? It should be done by now.

It's now done. I'm not sure whether it installed properly, though. Immediately after the update finished and I was able to log into Windows again, I tried to create a backup using Macrium, which gave me the bizarre error message "Failed - 0x8000ffff - Catastrophic failure - Retrying without VSS Writers". Does this mean there's something wrong with this installation of Windows now?

EDIT: I tried again, but this time Macrium didn't give me any error messages. Is there still reason for concern?

Press the Windows key + R and run 👉 ms-settings:windowsupdate-action

See whether there are pending updates.