SargonAelther: As I said, these ROKT ads that GOG is trialling only ever seem to appear on the checkout page AFTER you've completed the purchase. I'm not sure how many countries this is enabled in, but United Kingdom is confirmed.
They're not part of any installer, they're contained within the website. Maybe they'd show up on Galaxy too, I don't know, I buy everything via a browser.
I've seen the same ROKT ads when buying Cineworld tickets online. They'd also appear on the checkout page, once I've completed the purchase.
I've seen so many intrusive ads in my life so these ROKT ads are very mild in comparison.
Thanks for clarifying. I feel like an idiot. I was angry at a completely unrelated thing a little while ago. By time I got back to this thread and noticed the cookie button broken, I became confused. Then ranted.