Topic update.
Just finished the
Refresh your PC process. After about 25minutes, finally I logged in, of course all applications are gone, my personal files intact, but more important, the problem is gone. Thumbnails feature is working as it should now.
Thanks to all who helped and took the time to read and comment here.
I feel a little sad because I couldn't find a solution without reinstalling the system (that's practically what refresh pc does) but at least it got fixed.
Have a good evening.