On Steam there is an updated which features New Game+, that was released at the 19th of November.
When will it be released on GOG?

Where is the update?

The update on steam was 1 1/2 months ago!

Five months later - and still no update on GOG!

This is some pretty bad customer service!!!

And some pretty bad dev as well if they don't update their game by themselves. Did you try to contact the devs/publishers as well?

It has been updated now:
https://www.gog.com/forum/general/the_what_did_just_update_thread/post24020

I've seen it. Thanks!

I'm not sure how much it is the dev's fault or that of GOG.

In past discussions I've heard both sides blaming each other - so who knows.

From what I've read from Devs on these forums and elsewhere it's sort of an overhead problem.
If a game is build with steam in mind and/or using the steam tools, then there's extra work that has to be done to deploy it on another platform like GOG and that extra work applies to patches as well. It is not, I hear, as much work as writing the patch in the first place, but it is a substinal portion of the work.

This is, for example, the kind of thing that happened with Ancestors Legacy and why it was so massively delayed as a GOG release (there's more to it than that but I'm trying not to get sidetracked).

It seems there are some devs who don't know they'll have to do this additional work to make their game functional outside of a DRM'ed ecosystem and that's why we see a number of titles on GOG either get abandoned by the devs who make them or have massive delays in being updated when compared with their steam versions.

A note here, to be fair to all concerned, some of the smaller studios even if they are working entirely in good faith simply don't have the people to maintain simultainous patching unless they simply hold finished content and don't release the patch for either platform until they've done the work for both, which means longer deployment cycles.