Ok... for those who mocked me up and accused me of fearmongering and paranoid conspirationism... lets just deal with that for one message and then it will be settled, one way or the other.

1st:
Lets ignore each and any possible incident, bad behavior and overall malpractice against customers/users/product (seems we are rounded down to that role nowadays online) by the biggest internet companies of data mining and social BS or similar, for the past decade (lets name them GAFAM as in Google, Amazon, Facebook, Apple and Microsoft... but you can add more of course)

Let's ignore that those companies have so much financial weight, power and strength balance that they virtually have any leverage they want whenever they make deals with third party online services, business or companies in order for those ones to be granted some leftovers of GAFAM dishes, bread crumbles and bone to chew, as happy as they are with that.
(personal experience: i saw the extent of "droping trousers and bending over" behavior, short term financialy detrimental surrendering of one's usual policy, goals and anythin else a "small business" like, lets say, a european country's major phone operator + ISP was able to do just to please and comply to one of the GAFAM in order to be given the right to do business with them and gather some bread crumbles... i mean i saw that from the inside, as a tech employee... and it was quite scary)

Let's ignore all that, and that it never happened and so on... let's pretend those companies are benevolent and only want our best interest and to serve us genuinely.
Let's also pretend the recent Facebook "orchestrated" media scandal with/against EU court (which is just a masquerade) didn't happen

2nd:
Now lets use some FACT as you want them, and some reliable source, and also lets try to make all of that related to current topic, if you want:

Source is GOG's current pricavy policy terms, i dunno whenever it was changed nor how the previous iteration was worded so i'll only use the current one https://support.gog.com/hc/en-us/articles/212632109-Privacy-Policy
(is it a reliable official enough source for you all ? if not, then it's useless)

Pay attention to the occurences and paragraphs containing the word "partners". Let's agree that, as GOG decided to do some kind of business of any sort with Facebook (i think at least THAT is sort of official already, right, you wont deny this i hope) and so, Facebook can be seen as a "partner" regarding this Privacy Policy of GOG.

"2.5 For personal information contained in this Privacy Policy which is used by GOG, GOG is the data controller under European Union data protection legislation. For personal information contained in this Privacy Policy which is used by our Partners in connection with GOG services, then the relevant partner(s) will be the data controller under European Union data protection legislation."

This one is pure bonkers, as we already know for sure that whatever could happen, and regardless of that being already contested in EU court so far (yet no closure or final decision), FB clearly states in its TOS and EULA that all of their activities (including what they do with users personal data, or data they gather from their partners - aka here GOG - will only be put under authority of the country's court that is the most beneficial to them (some USA state's court, not sure if it"s california or whatever), despite whatever country the user or the business partner may be based, and regardless FB has a local antenna (a juridictional entity) in said country.
So, as soon as any kind of data ill be shared between FB and GOG, FB will be allowed to do whatever they want with it without any concern for EU legislation ! It already happened enough so far... we should know the drill.

"5.1 We may collect, process and use information about you in the following ways (either directly or via our Partners as explained above): (a) information you give us via GOG services; (b) information given when you contact us or report a problem with GOG services; and (c) we may also ask you to complete surveys that we use for research purposes, although you don't have to respond to them. We may collect this information via GOG services or trusted third parties connected with us for optional things like surveys or polls."

So that indicate the scope and sources of said user data GOG has fromus. Of course, i mean, this is a standard term here (but still, notice how the whole partners' role is slipped up inside). So when you create and use a user account on GOG, you have to give some info for the GOG service(s) to work properly. Note that the soon "big announcement" about the whole "happy family all friends" social fest will create new areas of collecting data through new services within GOG.

[i]"7.1 All information you provide to us is stored on our secure servers or those of our trusted partner services. (snip additional tech related part of the paragraph, and this is a standard and expected one). Once we have received your information, we will use strict procedures and security to prevent unauthorised access to our servers.
All information you provide to us is stored on our secure servers or those of our trusted partner services"[/i]

I'd like you to go dig out about what FB clearly states regarding data that are stored in their own infrastructures and whatever rights they grant themselves over it as soon as said data become stored there.
And however, the standard TOS listing the kind of "rights" and actions they grant themselves (or other GAFMA companies as well, as it is a typical standard TOS of those lot) is claimed to be required for technical necessities... but believe me, it is a bit overkill and cleverly worded in a too wide and vague way, because if you were to list and word the rights and action you would require only for tech's sake, it wouldnt have to be worded like this ! A convenient excuse, and it's already a foretaste of those big companies' obvious real intent and personal interest (protip: such goals and interests are NOT in your favor in any way... for those GAFAM folks, WE are the product... which usually had the self-excusing argument that their services are free... but it went beyond that, because same TOS apply to subscription-based or paying services and members as well)

[i]"9.2 GOG services may also offer you easy and optional access to GOG-approved partners’ services, e.g. the websites and games provided by our sister company CD PROJEKT RED. In order to do this, we will need to share some of your personal information (e.g. your email address) with them, as long as you agree to it. This personal information will be protected under our partner’s privacy policy.

You can use GOG services to access cool stuff from GOG-approved partners. We will need to share some personal information with them (which you control). It is up to you if you want to use your GOG account for this or not."[/i]

Now pay extra attention to this last one. As soon and as long as FB is in business with GOG, you have to consider that FB is one of those partners listed in this paragraph.
Notice that information shared from GOG to FB will then be "protected" (or "treated") under this partner's privacy policy. I let you enjoy the whole fun that is FB's privacy policy, and what they did so far regarding that.

Now last minute of your time, because this is WHERE we are getting back on current topic here: the second part of the paragraph. I will requote the sentence a second time here for the sake of reading:
"We will need to share some personal information with them (which you control). It is up to you if you want to use your GOG account for this or not."

HERE ! HERE lies the whole problem !
Because this is how it goes:
If you set your privacy settings to "public", then you obviously give your consent and agree to have your data shared by GOG to their partners (including FB)... But you changed the settings willingly.
If DEFAULT privacy settings is set to "public" from the start, then it still works/is seen as if you gave your consent as well
When said privacy settings of yours, whatever they had been switched as, get reset to "DEFAULT", probably through tech carelessness or laxism or... intentional way, it is also considered as if you gave your consent(and i say "when" and not "if" because it sure happened already... as i stated earlier, i, for example, turned the setting about how user can be searched to "Now Hidden" because of the random spamming friends requests wave we had less than two weeks ago, YET when i saw this thread created, it already was reverted back to "public")

So, if DEFAULT privacy settings are set to "public" for whatever sake for convenience of a majority, it also implies you will have any of your data (personal or anonymous) shared with partners of GOG but under THOSE PARTNERS" privacy policys, legislation and such.

Now just draw the conclusions and think back about is default settings set to "all public" is really a fair thing.