Since I didn't manage to find an answer in GOG Support Center, would anybody please teach me how to report spam?

There's this thread for that:
https://www.gog.com/forum/general/spambot_report_thread

Thank you, cose_vecchie. I appreciate your help.

Not that reporting there does much of anything. That entire account was reported weeks ago, along with various posts, including this one when it was made. And that tends to be the rule...

Hypothetically, you'd use a thread, but given that most of the staff don't appear to have administrative magic and/or take two week holidays randomly unannounced, this leaves most of the spam here unchecked and worse, indexed.

I see, Cavalary. Well, at least it's been reported. Hopefully, the staff will delete it someday. And I understand what you're saying, Darvond. Let's see what's going to happen in the near future. I thank you guys for the consideration and feedback. Take it easy and happy new year!

Thank you, have a great 2024, too!

A bit late but i want to thank chevkoch for this giveaway, very original. Gog, take note, that's how it's done.