In addition to my post before whose title I can't edit anymore, I want to provide a fix for the missing libsdl2-image-2.0-0 on newer Ubuntu 64 bit releases when running the actual game from the W2 launcher:

sudo apt install libsdl2-image-2.0-0:i386

edit: GOG added libgtk-x11-2.0.so.0 and libsdl2-image-2.0-0 under System Requirements on the store page. My thanks to their support staff.