pds41: You agree to receive the email (processing of personal data) and they also provide you with a free game (no processing of personal data).
octalot: What makes one of those necessary in order for GOG to perform the other one? You've put them together, but haven't argued why they have to be bundled.
It's a precondition. You get the game if you subscribe to the newsletter. It's like "getting a game because you give some money". The legal consideration can be considered the subscription.
[edit] To clarify, in the case we're looking at, you've got "Free game given as a reward to signing up for the newsletter". It's a single, indistinguishable requirement. You give consent for receiving a newsletter and they give you a game - one leads on to the other.
Remember, the primary consent you're giving (it's on the big green button) is to receive the marketing. The exact wording is:
"By clicking the 'Add to library' button, I agree to receive marketing communication from GOG sp. z.o.o. on my email address and through GOG services, connected to my GOG account, to get [GAME]. See our Privacy policy" This speaks to my point on the marketing forming the legal consideration.
If you wanted to separate the consent, it would be like this:
1. Do you agree to the processing of your personal data to receive a newsletter and marketing?
If YES, sign up email and proceed to 2. If NO, end process.
2. Do you agree to receive a free game?
If YES, award game to account. If NO, end process.
This two step is essentially what happens; it could be coded up, but ultimately would just mean that people have to click twice as the two steps aren't really separable.
On another tack, if you're looking at "Other Matters", these are intended to be much more distinct. For example, processing data to provide first party adverts (GoG's adverts) would likely need a distinct consent to setting up a GoG account (which is processing data to allow you to buy on the store). This is much more distinct than an inseparable consent to receive a newsletter in consideration of which you will be given a free game.