You have basically 3 options to create/link an account. Steam, google and an guest account. I used for the fist time steam and played for 4+ hours everything was fine. then on the 2nd start of thee game in loging screen was a popup like sign through steam, but i got the intro/tutorial movie and an NEW GAME ID. In loging screen my original steam 1 account got moved to guest account and i can´t link it with steam, since it is a new account (steam 2). I linked the guest account with google for now and request to delete steam 2 in game but they won´t let me link with steam (1) sice steam (2) exists for now.

to prevent this mess pleace make a guest account when you start the game for the first time, launch it 2-3 times and then link it with steam, but that´s only a guess from me how to work arround with thiss mess