Only after 3 days I was able to get Windows 10 2004, but with the sacrifice of the old installation, that was lost on the process of common update.
Since the update, I tried to do all kind of fixes (fixing the update and recovering the old installation) that Windows 10 allowed, but after so much pain I discovered that the original update procedure corrupted a lot of system files, including GUI components, so it was impossible to access UI also in Safe Mode.
Then, I had to create a new Windows 10 installation and now I am installing every software I lost and moving files and profiles moved to Windows.old.
Next upgrade I will pay attention to perform only 6 to 9 months after first users (test subjects) suffered enough after the upgrade.