It's on again - as per the title, subscribe to the newsletter and get the FREE items.
Thks to https://www.ozbargain.com.au/user/89239 for the instructions.
How to get offer:
Add GWENT Free(gog.com) to your GOG library (No need to download).
Link your GOG account with GWENT by Logging in your GOG account here(playgwent.com)
Subscribe here(gog.com) to claim The Witcher: Enhanced Edition and a GWENT Card Keg.
The game will be available in GOG Galaxy(gog.com) or under your account library(gog.com) in GOG.
Edit 0: Updated post with GWENT Download size [4.7 GB]. (Credit to: JonShannow)
Edit 1: Just need to add GWENT to GOG Library, no need to download (Credit to: Selenium)
Edit 2: Added clarified instructions on where to find the game after claiming it. (Credit to: Agret)