I just checkout out the latest giveaway and I got ads asking me to sign up for offers on hotels, food and other stuff. Is this actually coming from Gog or has some piece of malware got installed in my browser? I've never seen this sort of thing on Gog before.

Not just you.. got it for the first time here as well... ><

This is not malware. In the words of Clownski it is a new feature on our redeem page with the aim of enhancing your shopping experience and providing added value in quality free offers and trials to users

If you reject Marketing cookies these ads won't be shown.

I get a survey for gog after i checked out and bought the game only but i didn't fill it out yet since some question don't remember which.
I didn't feel like answering.

Also today i bought two games and wanted to pay with paysafecard but at the checkout the green button pay for your order was only spinning and didn't bring me to paysafecard site at least 3 tries.
Then i closed it went into my orders and then tried to check out and it worked on edge browser win 10

I think my ad blocker blocked that crap, because I took this giveaway but I didn't see any of that in my browser.

No one should ever browse any website without an effective ad blocker turned on. I also never see any ads on google nor on youtube either, even though I use both google and youtube every day.