Finished all the main quest and all the side quests.

Trying to play Gwent to win Geralt card from Thaler, but I have no option to play Gwent with him, when I meet him in Seven Inns.

Any ideas?

Sadly, console commands are the only way now.

Thanks, I read about it now.

The way I understand, I would have to just add the Geralt card directly through the console?
I mean, I cannot recreate the option of playing Gwent with Thaler through the console, right?

Yep. I don't think you can re-initialise a quest once it's completed.I'm no expert though