As the title suggests, Lutris is requiring me to sign in to GOG so that it can verify my ownership of the game. If my memory serves me well, I used to be able to simply click on the GOG version and then link it to the installation executable file that I downloaded from gog-games.com.
I already have the game installer, I just wanted to use the install script from the app.
My bad, I didn’t realize what community we’re in.