nvm

What is your achievement percentage in the My Progress section in GOG Galaxy? How about when you use a web browser to go to the game's details on your profile? Are there really no locked achievements?

Sometimes there's a small discrepancy between the percentage on the site versus GOG Galaxy. It seems to happen when the achievements total doesn't divide neatly (i.e. 46 achievements in this case, as opposed to say 50, which would've been 1 achievement = 2% progress). In those cases, you need one extra achievement to get that milestone on the site. But you say you've unlocked every achievement, so I guess that's not it.

The achievement milestones (25% / 50% / 90% / 100%) have been known not to get added to your profile on occasion. It's one of the earliest issues I contacted support about, years back. The response was that they don't have the tools to add those milestones manually. They evidently haven't done anything to prevent the issue in the first place, since it keeps happening.

both on gog and on galaxy it says 100% but I have to, as you suggested, go to the actual game details page to see that. ah so the milestone does sometimes not appear? interesting

Feel free to open a support ticket. You can tell the chatbot the issue is of type "other" twice to skip to that step. I don't expect they'll do anything, but I'd like to be pleasantly surprised.

Using a web browser, you can make posts to your profile. You can post text or an image to mark 100% completion of a game if you like.
Other than that, I don't think there are other options. There's only one chance to get the milestone card: when you unlock an achievement that brings you to that threshold. Support "refreshed" one of my achievements and that didn't help. The only alternative would've been to insist that they wipe my progress, so I can play the game from scratch, but I gave up on that idea.

To be fair, that one support ticket I mentioned was an unusual situation. There was a secret, unobtainable test achievement that had been left in there accidentally. When the developer deleted it, I found myself at 100% completion without having unlocked an achievement to get to that point. So maybe having support "refresh" one of your achievements would work in other cases.

right after this post I sent in a support request in the way you mentioned, telling the chatbot “other” twice (thanks for that by the way because I didn’t know you can type in your own message to the chatbot) and I got a reply very shortly after. Whatever it is that they did, it refreshed an achievement on my profile, but not for gwent. An achievement for rogue mage reappeared on my timeline even though it was already on it, but on an earlier date. I don’t know how this happened since the whole request was about normal Gwent. So I replied but nobody replied back, so I sent in a second support request, and just said “please refresh any achievement of mine for Gwent” and got a reply back minutes ago.

The achievement has been refreshed, but the banner for 100% completion did not appear. I’m fine with this. At the very least we gave it a shot. Thanks for all your help ;)