Additional info just discovered : when prompted for the email / skype id / phone number for the first time, I used my skype id, and apparently it is lnked to my old MS account, which was not completely translated to my new MS account. I’ve initiated the account recovery with live-dot-com, awaiting results at this moment.
So, what ideally is needed in FS2020 logon screen, is “use another account” button, so one could use another opportunity to enter a different id/email/phone.
Thanks for your support guys!
Mike