Hi everyone! Thanks for reading this! And yes, this problem has a workaround.
I have just reinstalled Windows 10 1909. When I entered my MS account (my email), I was asked to select one of 3 numbers in my iOS MS Authenticator app. I also set my fingerprint and face authentication. Everything run smoothly.
Later on, I have tried to access a folder on this computer from another one. However much I tried, I was unable to access. I checked Event Viewer Security log and it was clearly stated there "wrong user or password". Strange.
As I was sure I knew my username/password, I did one last thing: I used recovery options and rebooted into "Command Prompt" Mode. Voilà! It did not recognize my password.
To fix this, I changed my login to use a local account instead of MS account. I was asked for a username (which I select the same 5-letter one) and the same password of my MS account. Problem solved.
To bring things back to what it was before, I returned the login to use my MS account.
I would like to have someone to validate my workaround and perhaps to have someone inside MS empowered to fix this to solve it. It is really tricky!