Good day Sysnative WU,
Though I have not yet detected other dysfunctionings, it is indeed very likely the case that something got corrupted in my Office installation given how I know for sure that various other programs got corrupted in that initial event (and I am still far from having checked all of them).
Under those circumstances it would be abusing from your time and efforts (which so many others are in need of!) to push further. I will try a repair or a complete re-install of Office. Only if after that the Windows Update problem persists, then I will open a new thread.
For now, we can consider this thread closed very satisfactorily: the situation is much better than it was initially with many repairs done, most updates installed successfully, and I have a pretty certain idea of where the remaining problem lies and of how to fix it; And until I find the time to do it the computer is very useable.
I am still pretty baffled at how widespread files damages can be on a SSD due to power loss, but this is a lesson learned. I'll put in place a backup of the system for this computer.
I wish to thank you a lot for your time, efforts, and patience.
Keep up the good work!
Cheers