Ice_Mage: Could you please detail how you got the achievement?
1. I downgraded the game to 3.2.3320.
2. Started a new game with a blank Savegames folder.
3. I saved both before collecting the last egg and after, and backed up the entire save folder each time.
4. Neither set of saves unlocks the achievement when loaded in the latest version (3.3.3335). Deleting profile.dat before doing that didn't help either.
5. I downgraded again, loaded the last existing save, made a new save.
6. Updated again, loaded the last save. Still no achievement.
I can't keep going back and forth between versions hoping that the achievement unlocks at random. I've written to Daedalic support, but considering the last patch is 4 years old and the previous two games also have bugged achievements, I'm not very optimistic about a reply.
Yeah, it was annoying going back and forth for me as well. I think the one last thing that I tried which may contribute to the fix is using a savegame from the Daedalic support page.
https://www.daedalicsupport.com/en/games/goodbye-deponia/savegames.html 1. Get a savegame from the 3.2.4.3324 version. This may have been what worked for me. Use a save that still allows you to get all the eggs.
2. Then once you are sure the eggs are all found. Update the game to the latest version.
3. Go to the profile page where the eggs show up in the game.
This is where it unlocked for me. But I found that using a savegame that is naturally created from the game itself, was not working. Using a save from the site for the older version and then updating is somehow what worked for me. I hope this is helpful. Let me know if it works.