Ok, I was finally able to fix it by following the instructions I found there:
How to Create Administrator Account on Windows 10 When Can't Sign in
explaining how to create a new administrator...

From what I see when popping up command prompt, the drive letters are all upside down. My original windows drive is now at f:, and the drive where I have moved the users folder has also moved to a...

Thanks everybody for all the help. I really cannot understand why Microsoft does not propose as a standard configuration and as part of the standard installation of Windows 10 to specify User data...