You can also nudge the auto GPU detection setting off for the GoG version, which fixed it for me and didn't require downloading anything else.
Ignore this first step if you downloaded the game from gog.com website rather than through Galaxy:
Find where the game app is, right click > Show package contents. Go to Contents > Resources > game.
Right click Blackwell Unbound (or whichever game) > Show package contents.
Open Contents folder
Open Info.plist in a text editor.
Find the line "<key>Try To Use GPU Info</key>"
Edit the "true" BELOW this line to be "false" (no quotemarks).
Save file, quit editor, and run the game. You may have to dismiss the game settings dialog the first time.
*EDIT: got true and false the wrong way around. It should be true before you edit it, and you should change it to false ;)
dude you're a genius! :D How do people know this stuff! Ok for me it worked...