(STEAM) Can't pass the Xbox live logon screen!

You can install MSFS on any device, anywhere.
The only thing is, you can only log into one at a time, you cannot have more than one copy of MSFS running with your login.

You could also create a Zendesk support ticket from the “Support” tab at the top of any forum page.
In there, at the top, “Submit a Request”.
They should be able to give you some help.