Steam hides now the game list with the exception for friends (though even this doesn't look to me to be the case).
The change hurts sites, that work by parsing public profiles like Steamspy and achievement sites. GOG Connect surely gets affected by this as well.

Edit: Nvm, one can change it back to normal again. Still bad for other sites, but in case of Connect, a user is willing to make it public.

Edit 2: Link to announcement: https://steamcommunity.com/games/593110/announcements/detail/1667896941884942467
Sorry for the probably unnecessary posting. See it as a reminder to change the setting, if you want to use Connect or for other reasons.

My understanding is GOG connect shouldn't be impacted by this change because you have to log into your Steam account when using it (to link them together) which will still give GOG access to this info. Though I could be wrong of course.

Steam and gog might work out a deal between each other. I was already under the asumstion that there was some sorta deal or possibly gog has direct acces to your acount because they are linked

You just have to change your game list privacy setting to public when syncing with GOG Connect. It's the same with Steamgifts users and they're not really affected by this change.

This is a reasonable thought, but the Connect site states:
NOTE: Make sure your Steam Privacy Settings & Profile Status are set to public.

As Catshade said, pretty sure you can still set it to public right? You would just have to change it to public (I haven't really looked at the settings yet, but I think you can still change it to public).

The issue SteamSpy is having is that by default it's not public now, and they will never get enough people to change it to have any sort of accurate information about sales now. If everyone set their games to public, SteamSpy could still function but not everyone is going to do that, so it's a loss cause at this point.

I encountered my error, that resulted by not looking, if it is a changeable setting. I just saw the effects and made prematurely conclusions. My posting got already edited.
I would also like to edit the title, since it is now just clickbait.

It was impossible in my case to change "Game Details" to "Public" in Steam client.
But when I used browser, it changed without problems.
So, if you want to benefit from GOG Connect, you have to set "Game Details" to "Public" in profile settings.

Really stupid and harmful change in Steam, which no one was asking for.

I dun hv a prob changing in Steam Client so u may 1 check with Steam support regarding this.

Anyway, we can always set it to "Public" temporarily if we want link with GOG Connect so it shdn't be an issue.

While this may seem of a bit troublesome unless 1 dun mind setting it to "Public" always, it is still a gd move as it allows people to hv a choice & the benefits of hving privacy far outweighs the slight inconvenience 2 me.