Ok, i have already installed The Witcher 3 WH GotY Version...
via Gog Galaxy 2...

I played it 4 months ago (but i remember yesterday too, ~3 hours).

GoG Galaxy doesnt recognize the gema tlhough its installed.

I do not want to download the game again; (bc. i dont have enough space on disks, so why???

Steam on the other hand, you can change drive letters and it still recognizes it's bs...

So

Edit: It's solved... just add gog game and be happy...