Latest update.

Thanks, moreau. Yes, Jean’s programs and files are probably intact; the immediate problem appears to be a damaged Windows shell configuration, affecting both Start and the taskbar.
We are first checking and repairing Windows system files because update error 0x80073712 suggests component-store corruption. If that fails, the next step will be testing removal of the August cumulative update.
A taskbar-layout backup would indeed be helpful, although Windows unfortunately provides no simple built-in personal taskbar backup button. Once Jean’s system is operational, we can cover a practical backup method for the pinned shortcuts and relevant configuration.

Hello. Chat. As you might have gathered, I am 94 already and I had this morning a fall at home, and will be inop for a while playing with these devilish machine. I will be back. JP

Jean, I am very sorry to hear about your fall. Please put the computers aside and concentrate entirely on your recovery. The thread and machines can wait.
If you have not already been checked after the fall, please contact a healthcare professional or emergency services—particularly if you struck your head or feel unwell.
Take good care of yourself. We will continue exactly where we stopped whenever you are ready. Wishing you a comfortable and speedy recovery, Jean.