Hi all!

I wonder, is there any way to unlock achievements, after I finish the game?

I was running The Witcher 3 through regular .exe file (and use GOG Galaxy only to updates). And I thought, that when I load up my save file (with game completed) through Galaxy, it will update all my achievements, but opposite happens - none are present (just gray-out). I finish the game, so I cannot recreate many of them.

Is there any way to update them in Galaxy panel?

Achievements are not stored in your saved games. They are Galaxy only, and managed by Galaxy during gameplay, so if you don't run the game through Galaxy you don't get achievements.