The Sinking City is on sale on the Steam store again.
In the redist folder of the game there is a GOG folder with galaxy dlls.
Interesting. I just had a look at the Steam page and it kinda looks like this is the version of the game which was suddenly released a few months ago, after the game had been pulled from Steam. Y'know, the version which Frogwares have basically disavowed, claiming it's an unauthorized pirated copy uploaded by Nacon, the publisher.
The version on Steam also seems to have no paid DLC associated with it, but if I remember correctly, the original version released a few years ago did have paid DLC. So if this version comes to GOG at some point, be aware that it might not be the complete package originally released on Steam in 2019.