ipad could not be updated - an unknown error occurred (4000)

Hello,

see the title of this post for the nature of the issue:

I tried to update to ipadOS 12.3, and as part of the process, itunes started backing up my ipad, then returned an error message (which can be seen in the attached IPAD ERROR screenshot).

I have followed Apple's online guidance without success.

I also ran itunes diagnotics and the same error appeared in two different screens (see the NO IPAD FOUND screenshot). One apparent paradox here is that I successfully backed up my ipad as a procedure separate from the updating process, so actually, itunes DOES recognise my ipad.

My laptop is a Windows 10 machine. I upgraded Windows and restarted - twice.

I also updated itunes.

Also reset iPad pro 11 2018 about three times.

Only pro answers and solutions, please.

Many thanks