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iTunes version: Version 12.10.9.3

iOS upgrade 13.7 to 14.0

Issue always seemed to happen right after the backup was complete and message appeared indicating preparing iPhone for software upgrade.

What seemed to have worked is:

1. Disabled antivirus and firewall during upgrade(There was never this need to do so in previous versions of iTunes).

There are couple of other things I tried prior to this:

1. Changed the cable (old one was a bit worn out but that did not seem to be the issue).
2. Changed the USB port (silly but worth trying).
3. Re-installed iTunes (the latest version from Microsoft Store was acting funny as it did not have "Check for updates" option. Neither was it in the add/remove programs list. Had to uninstall from Start menu and re-installed using executable file from Apple).
4. Checked for latest update on Windows 10.
5. Disabled passcode temporarily during upgrade(there were even suggestions in some forums to play something on screen like video or music so it does not get locked).

Hope this helps anyone who faces the issue.

Had even tried this

6.Disabled USB connection blockage. iPhone will block USB connections one hour after the phone locks. If the backup and/or update takes a long time or if the phone wasn’t unlocked then it will block.

This is where it is Settings -> Touch ID & Passcode -> USB Accessories.

(Did not have to go to this feature in any previous upgrades).