Hi, I have the Intruder Edition on Steam and I used Connect to get Dusk on GOG, why does the Intruder Edition not come with it ?

Has something to do with the logistics of how the Steam API treats DLC, if I remember correctly. Since it doesn't list it as a game in most instances, it won't be recognized as part of your game library.

So, unfortunately (or fortunately, depending on how you look at it) you'll have to either buy the DLC upgrade here on GOG or be satisfied with the base game and just get the additional content via Steam since you have it there already when the occasion moves you to do so.