I just bought the DLC and am wondering where to find/activate it. The simple answer may be that I am too low level since I am only covenant level 5, but I don't see any indicator of this. When I select a new run, I can see the 6th faction, but it says "Clan Locked: Requires The Last Divinity DLC". I have seen mentions of a setting to toggle off the DLC, but I can't find anything in the settings. I also checked the DLC tab in the the GOG settings (Manage Install -> Configure... -> DLC), but no DLC show up there. I double checked my that I got the receipt that says that I bought it. The only other thing that I can think of is that I got the base game for free through Amazon Prime, but GOG advertised the DLC on the game page and let me buy it.

I don't know how galaxy works with dlc installation so I cant help there. You should be able to install dlc for games you got from amazon. It sounds to me that maybe something with the installation went wrong? Maybe just try to completely reinstall both the base game and dlc?

The DLC toggle is in the top right corner of the main screen.

I came back and checked a couple days later and everything was available. I am not sure what was up.