As with many other games on GOG, at least three simple achievements that should be obtainable for most of the people by playing the game normally (not even trying to 100% it) are broken: "Outbreak", "Obsessive", "KPD! Open Up!". It is evident form their extremely low unlock rate as compared to more obscure ones targeted at completionists.

When you are logged into gog.com, you should look next to your profile name under "activity feed". From there you will see four tabs, one of them is "games", clicking on each game that you own will show its global achievement rates on GOG as well as which ones you have unlocked. The unlocks show up in the said feed, so you can directly go from the feed to a specific game.

However, i have not found a way to see achievement stats on GOG for the games that i don't own. The community features on GOG are relatively very poor as compared to Steam.

Thank you very much, that's a nice tip!
+1 on the lack of poor stat (so far). I'm using other tools such as Exophase to gather come useful stats about achievements in the meantime.

For Observer SR, indeed 1 only see one achievement unlock but the stat are not reliable (only 1 player registered): https://www.exophase.com/game/observer-system-redux-gog/achievements/

yep, can confirm all still broken over a year later.