Please post in one of these threads for posterity:

https://www.gog.com/forum/general/silent_optout_spooky_addition_to_gog (<- GOG staff posted here)
https://www.gog.com/forum/general/when_do_you_transfer_my_personal_data_to_google_and_facebook

My advice would be to stop claiming giveaways.

Unless your e-mail address is a string of gibberish, you're vulnerable to dictionary spamming. As for the "trusted partners" option under Subscriptions:
"We will use our Trusted Partners services (such as Google Ads and Meta ads - see the list and more details here) to send you marketing communications about cool stuff happening on GOG, tailored to your interests. Keep in mind unchecking this does not mean you would not never receive any GOG ad - they will just be less tailored to your interests."

So there's no doubt when you get an e-mail as a result of your GOG marketing preferences, because they're clearly labeled.

Depends on what you mean by spam emails. Whom did it claim it come from? What did it say?

And you somehow thought that was going to stop your information from being shared?

How do you know your information wasn't shared in the very same "instant" in which you were in the process of "turning it off?'

No offense, but trusting your information to remain safe after you have (electronically) signed away your rights to it (even temporarily) wasn't a wise decision.

Sadly, many other GOG customers also seem to have made that same mistake. GOG received very little backlash against this change, and every official "giveaway" thread since the "information sharing" started is still full of many members posting messages like "Thanks for the free game, GOG!", and almost no negative feedback in the threads after the first game for which it happened.

While I do not deny the possibility, it could also still be just a coincidence. you can only know that they got it from GOG if you ask them and they say "yes". Just because one happened after the other does not necessarily connect them.
Do you know if the ones who sent you the mails are the same ones that are considered to be trusted partners?

Maybe it was a coincidence then as this didn't mention GOG at all.

It just seemed odd that it was sent to my GOG address which I've never used elsewhere and has never had any spam before. I registered in 2013 with the address and since then the only messages I have ever received to it was from GOG which was why a red flag was raised for me. Oh, the joys of the internet :)