I remember looking this up the last time there was a freebie from Fanatical, I think the info they get from Steam is quite little (I can't now find a reference but I think it's username and a little more but no real name or email or any of the important stuff).

You could probably try creating a brand new Steam account with no info and linking that one to Fanatical to get the game, you could then use family sharing to make it available to your real account.