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.
Personally I use innoextract on the installer, add the game to bottles or even steam library if I add it to my deck and play. No need to even bother double clicking installers, it’s doing the same process of extraction with dumb banners I don’t care about.