I completed thronebreaker: a witcher tales months ago and am currently playing the gwent game. I noticed that i barely got any reward from my thronebreaker play in gwent, whereas i finished almost everything in thronebreaker. I suppose this is linked with me not unlocking the gog achievements of thronebreaker, because i played the game offline back then and didn't noticed it. Is there a way to claim the gog achievements and then get rewards in gwent ?

thanks for any reply

To unlock an achievement, both the GOG Galaxy executables¹ and the game executable need access to the Internet, for the entire duration you're playing the game. Otherwise, you'll have to load a previous save² and try again. Very few games will save your achievement progress locally and unlock them when you next go online.

¹ article applies to any online feature, including achievements
² article applies to any game with achievements

no they don't carry over
if you own / play a game on Gog as well as whoever else, its only the achievements and time spent on Gog that unlocks in Gog