Another follow up up. The mystery gets darker.
I was intrigued by what was written by a user with a problem similar to ours (even if it referred to error 0x80070005). He wrote that he had found some differences if logged with a different account. I usually log on to the machine with my microsoft account, so I created another local user and logged on with that. I do not like to draw conclusions, but the fact is that with that account microsoft store and photos work without a glitch. If this is not enough, reverting to logon with microsoft account, now both Store and photos work.
I don't understand what is going on here, maybe some expert can draw the proper conclusions. Now I am still stuck with the update error, but this is a different story... or is it?