Well, not sure what to say. It is working fine on my end. I am using Edge, if it is relevant.

Maybe I'm using firefox. Let me test.

Edit: Still not showing up for me.

For me at least it appears to only be broken on firefox. If I go to the store via the galaxy app then I can hide my owned titles. If I sign in using Edge I can see the box to hide my owned titles.

Seems like GOG did something and didn't test with non Chromium based browsers.

The Discounted Games Wishlist filter is still broken on Firefox. There used to be options on the upper-left side to only show games in the Wishlist and to omit already purchased games from the list. But all of those options have been gone for days.

On
https://www.gog.com/en/games and
https://www.gog.com/en/promo/weekly_deals_3_october and
https://www.gog.com/en/promo/20231019_adrenaline_rush
it doesn't show my games marked as owned.

However - after refreshing the pages once, they showed my games as owned.

Out of curiosity, I then refreshed the pages again - and the games were not marked anymore (and several attempts to refresh didn't change that).

With all that's going on lately here on GOG, it really seems as if they finally reached the point, where duct tape and spittle alone aren't enough anymore, to keep the website goin'.

When you go to a sale page, for example the THQ publisher sale, the only two options on the left of the list are Show only discounted and Hide DLCs and extras.
There should more options appear, like Hide owned games, show only wishlisted games, etc.

Also the actual list of the games do not show as owned or not, so you can't tell if a game that is on sale is actually a game you already have, so the only way to know is that either you remember if you own a game, or if you one by one go to each game store page and see there.
This makes it a chore to check the sales and makes me not want to even consider buying a game.
I hope that is clear enough for you.

I can think in two possibilities. Something was changed in the site code and non Chromium Browsers were not properly tested

Or something AdBlocker related. Maybe it is giving problems with some of the site features. Specially the newer implemented ones.
I tried to enable my adblocker and it resets/closes itself when refreshing, so I can not test it properly, maybe I tweaked something in the past for the GOG site to disable it. Not really sure.

I disabled uBlock Origin on GOG and refreshed the page, the issue persists. So it's nothing to do with adblockers.

Did the same with Privacy Badger, with the same result and conclusion.

I wonder if (within a browser) spoofing a GOG Galaxy user-agent might assist in determining why the client is unaffected.

Does anyone have an up-to-date user-agent for it? I only have old versions from circa 2015 (the most-recent attempt at using the client).

I'm not sure if everyone reporting here knows exactly what to look for?
The problem is only visible in the catalog grid or list view, where there are filter options next to it.
For example in GOG's general catalog here: https://www.gog.com/en/games
Also on sales pages but you have to scroll down beyond the featured bestsellers. For example here: Cozy Autumn Sale.
edit: It concerns only the website, not the Galaxy client.


What's NOT WORKING?
It seems like the catalog view can't reference our account data and games library.
- "owned" and "wishlisted" labels are missing
- filter options concerning the wishlist and owned games are missing, too

What's STILL WORKING?
Still working is everything that's not connected to a specific account
- "early access", "pre-order" and "soon" labels are shown in the catalog!
- filter options for release status, DLCs and free games etc are working!

IMPORTANT:
You cannot tell the difference if you aren't logged into your account!
If you are browsing as an anonymous visitor, then there simply isn't a wishlist or a games library available...

Also:
The catalog's behavior is pretty shaky. Most times, the catalog won't show 'owned' labels or wishlist filters.
If it does for some obscure reason, then it's only temporary.
If you think it's working, try reloading the page a few times and compare.

-----------------------
I did a bit of testing myself:

uBlock Origin enabled or disabled - NO DIFFERENCE.
(edit to clarify: plug-in completely disabled, not just an exception for Gog.)
(no other Adblocker or similar installed)

Firefox vs Chrome, both times logged into my Account - NO DIFFERENCE.

You can add Edge, as well.

P.S. Nice summary. You might want to add that the bug is absent from galaxy.

I have tried the main catalog (indeed www.gog.com/en/games) and everything seems to be working as intended. As in the sales pages I tried before, the games are properly marked as "in library" "wishlisted" etc... The tick to "hide owned games" is there and it works. Obviously I am logged to my account and using my Edge web browser.

Opera here too.

I have noticed something. When refreshing the page and it is loading, the "in my library", "wishlisted" labels and some tickables like the "hide owned products" etc... are not there during the process until they are completely loaded, but others are ( for me it is some seconds, I always accepted it because my slow card, laptop and average wifi).

Apparently your behaviour is like the page had not completely finished loading and stood still in that way. Weird.