ISSUE SOLVED.
The first thing is that I did not update the plugin first and then the template, but I directly loaded the framework downloaded from the joomshaper site.
This created the problem.
HOW DID I SOLVE?
Having a backup copy, unfortunately a month old, I restored it to another location on the server.
So I did the update correctly, first the plugin and after the template.
I copied the template folder on the original site and replaced it with the old corrupt one.
Everything is back in place, and updated, in the best way.
ADVICE
- Always have recent backups
- Always update the framework plugin first and then the template.
Thanks for your attention