Ice_Mage: I think you need to be subscribed to the newsletter for that. Try this:
1. Exit GOG Galaxy.
2. In a browser, go to your subscriptions and check every box there.
3. See if the banner shows up in the Recent category in GOG Galaxy.

If that doesn't work,
1. Add GWENT: The Witcher Card Game to your account for free, if you don't already have it.
2. Go to https://www.gog.com/gwent-welcome-bonus
3. Click the Subscribe & Claim button to subscribe to the newsletter (that you're already subscribed to) and get your Gwent bonus.
4. At the same time, the above reveals a button on the right side that gives you a -100% discount for The Witcher. Add the game to your shopping cart and complete the purchase to get it for free (or get a free gift code to give away, if you already own it). I tested this moments ago and it still works.

Ice_Mage: I think you need to be subscribed to the newsletter for that. Try this:
1. Exit GOG Galaxy.
2. In a browser, go to your subscriptions and check every box there.
3. See if the banner shows up in the Recent category in GOG Galaxy.

If that doesn't work,
1. Add GWENT: The Witcher Card Game to your account for free, if you don't already have it.
2. Go to https://www.gog.com/gwent-welcome-bonus
3. Click the Subscribe & Claim button to subscribe to the newsletter (that you're already subscribed to) and get your Gwent bonus.
4. At the same time, the above reveals a button on the right side that gives you a -100% discount for The Witcher. Add the game to your shopping cart and complete the purchase to get it for free (or get a free gift code to give away, if you already own it). I tested this moments ago and it still works.

StarTiger63: You're a star mate, got it all installed your way, Thanks very much.

Red_Chaos1: It no longer works, the page you get when going to the link you supplied does not give a page like you show for step 3. The button is merely to download the installer and nothing else. No new button appears after, just the page telling you to run the installer and follow the directions.

Ice_Mage: I still see the Subscribe & Claim button when I'm not logged in, so I don't know what to tell you. Open a new support ticket, if you haven't already. (When I'm logged in, I see a message that I've claimed the Gwent keg and The Witcher)

Red_Chaos1: I'd claimed the GWENT thing, but it didn't show up in Galaxy. Silly me, I guess I was supposed to somehow know it needed to be installed standalone (not blaming you for that detail).