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.
Give Me Convenience or Give Me Death
Itch.io gives the convenience. although the UI is far from good, you straight-up get the zip folders with the game itself if you download from your browser, and their launcher still adopts no drm.