Asked GOG support about this, answer: issue seems to be on developer's side, they've been notified but once more no promises.

Still think it's not alright for a store page to list achievements as a feature. It's been two years, at least GOG could add a warning about this.

Spent 36 hours playing this game, and no achievements unlocked; any solution?

Still not working. The game is advertised as having achievements at the time of this post, and for years achievements aren't working. What recurse do consumers have for purchasing a game with advertised missing features, when GoG and the developers refuse to fix this for years?

Fix the bugged achievements, or do what's right for consumers who purchased this expecting advertised working achievements.

So is the achievements feature in this game pretty much abandoned then? I've seen people talking about them for years.