Nice work! I wish I could help you but debugging js is above by capabilities. :-(

All I could do was verify that neither a specific browser (Firefox, Chrome, Edge) nor disabling ad-blockers (AdBlock, uBlock Origin) make any difference.

Thanks! Maybe there is a way you can help. If you've got Galaxy on your system, could you look to see whether an actual file called 'accessTokenClient.js' exists? And if so, can you copy its contents to a .txt file, upload it to Pastebin or any other text-sharing website, and provide the link?

No such file. Neither in the program directory itself nor among various user settings directories.

A temporary solution by Palestine:
https://www.gog.com/forum/general/temporary_workaround_for_missing_store_options_and_labels

P.S. Works for some, not for others, for reasons that are unclear at the moment.
P.P.S. Using Ctrl+F5 to force reload seems to make it work for everyone.

Does not work for me.
I still am unable to see either the filtering options or the labels marking the owned/wishlisted games.

Thanks for your help. Even though there is nothing to compare it to my altered version, the real problem remains how to import and use it in Firefox and other browsers to permanently override the original, as is possible in Vivaldi.

The filters do work for me in Edge, which I prefer not to use, without making any changes. Accepting all cookies and allowing the execution of .js code for the domain, done. The page still needs occasional refreshing, but it's less frequent than with any of the other methods I've found working on my end, and it's less involved, so that could be another option.

For now, I'm unsure of how to proceed or whether I should even consider it, because without official input on what they are doing to fix it on their end, any solution will either be temporary and work for some of us or not work at all.

It did for me, but only after forcing a full page refresh while on the embed portion of the site

Same. Initial load, no go, F5, no go, Ctrl+F5, works.

Braggadar, and Cavalary, thank you for your feedback!
I am so glad that forcing the browser to ignore old cache was the solution for both of you. I have updated the thread accordingly.

A week has passed since the latest bug has emerged (broken catalogue/sale filters and markers) on 16/10 --- and still no solution from GOG.

Meanwhile, Palestine has found a temporary workaround that can be summarised by:
- on any failing catalogue/sale page, change the "www" in the URL to "embed", and press enter
- if this is not enough, press Ctrl+F5 to force reload the page

The above has been fixed.

Searching in the Orders history does not work for me. No matter what I enter as search term, the page is spinning for a while and then always returns: "No results found".

Works fine here. Click on Orders History and make sure everythink is checked. If it is try another browser.

Works fine here too.