Is this game anyhow supported in GOG?
The game is vastly outdated comparing to other platforms...

On the steam forum the developers mentioned that GOG only gets the major updates and that the smaller beta patches only come to steam. This in part because they get a lot more feedback on the steam forums. And looking at the activity on this GOG Gordian Quest forum they are not exactly wrong

Currently there have been a lot of small patches on steam (in the 98 branch). Until that slows down I don't expect updates here. Although I do think we should have gotten the final build in the 97 branch (97k) since that seems to me to match their criteria for a GOG update