As Dan guessed, you have a subscription, and you would sign in with your gmail account.
I mentioned in the support reply that the day after you subscribed we released the 2020 version. You’re entitled to that one if you like, no need to download 2019 again. It’s different to 2019, mainly in that it has an actual installer, instead of dragging the folder to Applications. You don’t have to remove 2019, if you need that for compatibility with extensions, or any other reason.