At some recourses, I found out that GoG version of SS4 has implemented Achievements, but at the same time on the official game page at GoG store Achievements are absent. So I want to ask are Achievements available for GoG Gamers?

From what I understand, they were initially there and working, but after a game update they stopped working altogether.

I guess GOG removed the tag following customer complaints, the problem is that they are still visible, mocking the player who can't get them. Ideally, those incompetents at Kalypso Media Digital should fix them, but they don't seem inclined to do so for now.