Neither did I.
I bought the game through steam.
However, FS2020 uses the Xbox servers to handle user registration/profiles. - this is your “gamertag” it’s an Xbox account NOT your Microsoft account.
If you created or logged in with an account when you originally installed and first started the game ever then your marketplace purchases are associated with it and you will need to log into FS2020 with this same account in order for cloud saved data and marketplace purchases to link to your new install.