mantazzo: Can confirm that even after 1.03c update the Editor still crashes unfortunately. Unsure why. Tried with GOG Galaxy turned off, same issue.

EDIT: I think I found the culprit, though it's not a very nice solution so far.
After a few testing attempts, I found out that Editor is dependant on... steam_api.dll. Yes - Steam DLL stops the Editor from launching. As to why - probably because Steam probably detects that we do not own the game (unless you also have the game on Steam, which makes this redundant..?) and the app just straight up crashes. However, with no DLL in the folder the Editor will fail to launch also. I had to "install a Steam Emulator dll" (which is why I said the solution is not very nice) to get the Editor finally working on GOG version.

tl;dr - Editor on GOG version is most likely broken due to dependancy on Steam DLL.