Well I almost don't believe it.

For the first time in ages that Free games link in my last post above, actually worked properly.

Have GOG maybe been paying attention and fixed or restored something?
If so, it hasn't been extended (or not yet) to the main front page, as my owned games are still not showing the IN LIBRARY label.

I'll keep my fingers crossed and hope for the best.

At least some of my issues with GOG web pages appear to be browser related, so either due to Chrome or Brave (Chrome clone). I'm currently using Edge on a different PC and so far things seem fine.

No changes to the store main page, but noteworthy nonetheless:

Still issues to iron out, it looks like:

That is a nice addition.

One minor gripe (of course):
dear GOG team...why not make it so, that the game's page opens in a new tab, if I click on the thumbnail?

Well, you can always middle-click. Or shift+click. And it's not like in the catalog's default view or on the front page where you need to wait a moment for that annoying expanded info to open before you can middle-click to open in a new tab. On the other hand, can't so easily make it open in the same tab if you prefer that but it's made to open in a new one, and a strict popup blocker may block automatic new tab openings.