is internal editor in linux gog version?
Apologies for late answer.
The internal tooling are present in all computer versions including Linux GOG, you need to enable them in the .ini file and then press F to leave Fullscreen mode. There are some instructions on the Steam forum. Please bear in mind they come with no support/guarantee and in fact I can only pretty much guarantee that they are available mostly "because we can" rather than "because it is really super useful". But if you like to explore mysterious undocumented tools it may be fun to explore :)